• 3G: 3G Stands for 3rd-generation. Analog cellular phones were the first generation. Digital marked phones were the second generation.
  3G is loosely defined, but generally includes high data speeds, always-on data access, and greater voice capacity. They enable such advanced features as live, streaming video.  There are several different 3G technology standards. The most prevalent is UMTS, which is based on WCDMA. (WCDMA and UMTS are often used interchangeably.)
• Aftermarket: Classified for items made by a third party manufacturer to be used for another company's product(s).
• Airplane Mode: Some phones and other wireless devices have a special "airplane mode" that turns off just the wireless radio parts of the device, for safe use on an airplane.  Most airlines and many governments ban the use of wireless radio devices during flight, to prevent interference with the plane's radio and navigation systems.  Airplane mode therefore allows the user to safely use the non-wireless functions of a phone (such as games or organizer functions) on an airplane during flight.  However, not all airlines have policies that accommodate devices with airplane mode; some airlines still ban the use of all phones during flight.
• Alarm Feature:  An alarm feature which can be set for a specific time and date or can used as a daily alarm.
  If the phone has a calendar feature, the alarm feature may be integrated with that, so an alarm is simply a calendar event. Although some phones with a calendar feature also have a separate alarm feature.
• Alphanumeric Display: Consisting of letters (A-Z) and numbers (0-9).
• AMPS (Advanced Mobile Phone System): A standard for analogue mobile systems. Used in North America, Latin America, Australia and parts of Russia and Asia.
• Band or Bandwidth: In wireless communication, band refers to a contiguous range of radio frequencies. Currently, wireless communication service providers primarily use the 1900 MHz and sometimes the 850 MHz in the United States . GSM providers outside of the U.S. use 900 MHz and/or 1800MHz.
• Bluetooth: A wireless personal area network (PAN) specification that connects phones, computers, appliances, etc. over short distances without wires by using low power radio frequencies.  Bluetooth allows you to leave your phone in your pocket, while talking on your phone with a Bluetooth headset - without wires. You can also exchange contact or scheduling information with other Bluetooth-enabled phones nearby, or send such information to a nearby Bluetooth-enabled printer.  Bluetooth functionality is divided into separate types of connections known as "profiles". Each of the various scenarios outlined above involve a different profile. Not all Bluetooth devices support all profiles.  Most phones support the Headset and Handsfree profiles, for connecting the phones to headsets and car kits, respectively. But not all phones support the Object Exchange (OBEX) profile, which lets you transfer files (like photos and video clips) to and from other devices. Another profile supported by only some phones is Dial-Up Networking (DUN), which lets you connect a laptop or PDA to the Internet via the phone. Other optional profiles support connecting to printers and keyboards, etc.
  Bluetooth is named for the 10th century Viking King Harald Bluetooth, a Danish king who conquered Norway.
• Calendar Feature:  Calendar feature allows you to store scheduling and event information in your phone. Some phones also offer the ability to sound an alert to remind you of upcoming events.
• CDMA (Code Division Multiple Access): A technology for digital transmission of radio signals between, for example, a mobile telephone and a base station. The system uses the same frequency to allow multiple conversations. Each conversation is cut into snippets and then remodulated in reassembled in the other end.
• Custom Graphics:  Custom Graphics is a customization feature that allows the user to set custom graphics to appear on the phone's display. The graphics may be downloaded via a cable from a computer, downloaded via Wireless Internet, or sent to the phone via SMS.  Various phones allow the graphics to used in different ways. Some ways include: as the main or background graphic during standby, as the background in menus, as the main graphic during an incoming call, and as a screen saver after the phone has been idle for a certain period of time.
  Some phones also provide options such as cropping and sizing, and superimposing and positioning text over the graphic. Some phones include built-in graphic editors.  In addition, some phones allow exchanging graphics with other phones via SMS, EMS , and/or MMS.
  A related but distinct feature is Picture ID, which is where a phone allows custom graphics to be assigned to individual phone book entries, to be displayed when receiving an incoming call from that number.
• Custom Ringtones: This means that the phone has selectable ringtones that can be set to a custom melody (or "ringer") that you can change to something other than the ringtones included with the phone.  Some phones include a built-in "composer" that let you enter the notes manually and create your own ringtone right on the phone.
  Others require that the ringtone be created elsewhere and downloaded to your phone via special SMS, EMS , or MMS messages, or via Wireless Internet.
  Ringtones can also sometimes be transferred in the form of a file from another device, such as a phone, PDA, or PC, via a cable, infrared, or Bluetooth.
• Digital Zoom:  A software feature that has trade-offs in image size or quality. Many camera phones offer digital zoom.
• Dual band: Dual band mobile phones can work on networks operating different frequency bands. Often urban areas operate on 1800, while suburbs use the 900-band. This is especially useful if you travel abroad. Some phones are able to switch between GSM 900, 1800, 1900 (tri-band) allowing you full coverage in Europe, America and Asia.
• EDGE:  Enhanced Data rates for Global Evolution. A technology being promoted by the TDMA and GSM communities that is capable of both voice and 3G data rates up to 384 Kbps. The standard is based on GSM standard and uses TDMA multiplexing technology.  EDGE must be supported by your carrier, in your area, with an EDGE enabled phone or PDA.
• Email Client: Some phones include a full email client that can connect directly to standard POP and/or IMAP email servers, via a wireless data connection and the Internet.  Your carrier must support this feature and it must be activated as part of your service plan.
• EMS: EMS standard for Enhanced Messaging Service. It is system that has evolved from the standard SMS messaging you my be used to, and allows standard ringtones and graphics to be sent to and between phones.
• ESN: Electronic Serial Number.
• Expansion Card:  Expansion cards can be used to add memory or features to a phone. Extra memory can be used to store and transfer photos, videos, music, computer files, or backups of phone data such as the phone book and calendar.
  There are several different types of cards. Each has a different shape and size, but cards from a phone can also be used with other devices which use the same type of card. Such devices might include handhelds, digital cameras, and MP3 music players.  Some phones will only work with memory cards up to a certain size.
• Firmware: Firmware is something in-between "hardware" and "software" - hence the name "firmware".
  Hardware, in high-tech devices like phones, is any part of the phone that is physical and cannot be changed unless physically replaced. For example, Verizon phones are CDMA, while Cingular phones are GSM. The two systems are incompatible. The Verizon phone contains a CDMA chip that was designed specifically to deal with CDMA. It is permanently wired that way, and could never be changed to GSM with any kind of upgrade.
  Software, meanwhile, refers to things that can be changed. In a computer, you can of course load new software whenever you want. You can even load a whole new operating system. The software is stored in memory chips while in use, but as soon as the computer is turned off, whatever was in the memory chips is gone, but a copy is saved on the hard disk.
  Phones need to store various non-permanent things, too, such as an operating system, roaming instructions, and your phone book. But there is no room for a disk of any kind, and it wouldn't be good if your phone lost its operating system (and thus became useless) every time you turned it off.
  This is where firmware comes in, firmware uses special memory chips that can hold information even when the phone is turned off and battery-less. It's sort of like hardware, because it acts just like a permanently-wired chip, but it's also like software because it can be changed at any time.
  So firmware is technically how your phone stores its phone book, but when most people here talk about firmware, they are talking about the roaming instructions (PRL) or operating system.
  You can have your PRL updated and your phone will be able to roam in new areas. Sometimes operating system updates are available that fix bugs in the way the phone works. Sometimes updates even add new features, such as ERI or 2-way text messaging. These are all firmware updates.
• Frequency: The rate at which a wave alternates, usually measured in Hertz (Hz) - cycles per second. Also the way to note a general location on the radio frequency spectrum such as 850 MHz, 900 MHz 1900 MHz, 2100 MHz (UMTS).
• GPRS (General Packet Radio Service): A packet-linked technology that may enable high-speed (up to 115 kilobits per second) access to wireless Internet in a GSM network. GPRS is IP-based, and may allow users to be online 24 hours. General Packet Radio Service (GPRS) is an enhancement to existing GSM and TDMA networks that introduces packet data transmission, enabling "always on" mobility. This means that users can choose to be permanently logged on to e-mail, Internet access and other services, but do not have to pay for these services unless sending or receiving information. When EDGE is added to GPRS, these data rates will increase up to 384kbit/s.GPRS will be implemented by adding new packet data nodes and upgrading existing nodes to provide a routing path for packet data between the mobile terminal and a gateway node. The gateway node will provide interworking with external packet data networks for access to the Internet and intranets.
• GPS: Global Position System. Based on US defense satellite system, enables tracking of individuals. This technology may prove helpful when navigating a car in the city, or help emergency rescue-team to locate the person in need of help.
• GSM (Global System for Mobile Communications): The world's most widely used mobile system. Used on the 900 MHz and 1800 MHz frequencies in Europe, Asia and Australia, and the MHz 1900 frequency in America.
• GSM Unlocked: Unlocked GSM phones are wireless phones which are not subsidized and locked by any service provider. This means that the phone will work with any GSM network in the world that carries the band/frequencies specified for a particular phone. Please contact your service provider if you are not sure about the frequencies they carry. Unlocked GSM Phones will only work on a GSM Platform. This means that your Wireless Service Provider has to be a GSM Service Provider.
• IMEI: The IMEI (International Mobile Equipment Identity) is a 15 digit Code used to identify the GSM/DCS/PCS phone to the network.
• IrDA: Some mobile devices incorporate IrDA® ports for cable free data transmission, it is not, however the same as Bluetooth as the ports need to be lined up during data transmission.
• JAVA (J2ME): A high-level programming language developed by Sun Microsystems. Java was originally called OAK, and was designed for handheld devices and set-top boxes. Oak was unsuccessful so in 1995 Sun changed the name to Java and modified the language to take advantage of the burgeoning World Wide Web. Java is an object-oriented language similar to C++, but simplified to eliminate language features that cause common programming errors. Java source code files (files with a .java extension) are compiled into a format called bytecode (files with a .class extension), which can then be executed by a Java interpreter. Compiled Java code can run on most computers because Java interpreters and runtime environments, known as Java Virtual Machines (VMs), exist for most operating systems, including UNIX, the Macintosh OS, and Windows. Bytecode can also be converted directly into machine language instructions by a just-in-time compiler (JIT). Java is a general purpose programming language with a number of features that make the language well suited for use on the World Wide Web. Small Java applications are called Java applets and can be downloaded from a Web server and run on your computer by a Java-compatible Web browser, such as Netscape Navigator or Microsoft Internet Explorer.
• Keyguard/Keylock: This mobile phone feature allows the user to disable (lock) the keys so that a number will not accidentally be dialed while the phone is in your pocket or purse. A special key combination, unlikely to be pressed accidentally, is typically used to unlock the keys.
• LCD: Liquid Crystal Display. LCD displays utilize two sheets of polarizing material with a liquid crystal solution between them. An electric current passed through the liquid causes the crystals to align so that light cannot pass through them.
  Monochrome LCDs in phones usually have both a backlight and a reflective backing, allowing them to be equally usable in both bright light and complete darkness.
  Color LCDs come in many types. STN, TFT, and TFD are several common technologies used.
• Li-Ion Battery:  Lithium-Ion type of battery, often used to power wireless communication devices. Considered superior to NiCd and NiMH batteries - they are lighter weight, have a relatively long cycle life and generally do not suffer from "memory" effect.
• Li-Po Battery: Lithium Polymer type of battery. Similar to Li-Ion batteries, but slightely lighter and the batteries can be molded to any shape.
• MB (Megabyte): 1MB = 1024 kilobytes (KB)
• MIDI:  MIDI (Musical Instrument Digital Interface) is a set of specifications for describing music. Instead of capturing and storing the sound of music, MIDI information describes the instruments, notes, and timing of the music, which can then be recreated on MIDI-capable devices.
  A simple MIDI device might only reproduce the notes, while more sophisticated devices can create realistic-sounding music by synthesizing individual instruments. If multiple instruments can be recreated simultaneously, this is called polyphony (see Polyphonic Ringtones).
  As an industry-standard, efficient file format for describing music, MIDI is often used for custom ringtones. Standard MIDI files can be transferred to a MIDI-capable phone and used as a ringtone.
• MiniSD: A type of removable flash memory card.  Like any flash memory card, it can be used to store various types of files, including photos, videos, music, or software.  As the name implies, miniSD is similar to the SD format, but smaller.  MiniSD is smaller than MMC and SD, but larger than TransFlash, which is also called microSD.  MiniSD is close in size to the competing RS-MMC format.
• MMS: MMS stands for Multimedia Messaging Service. A multimedia message can contain text, pictures, animations, melodies and sound. You can also send contacts, event entries and sound recordings as attachments.
• MP3:   Short for MPEG Layer 3.
  MP3 is a common file format for music and other audio content. It is commonly used on the Internet, on PCs, and on portable devices, including dedicated music players and phones with music player functionality.
  Some phones that do not have full music-player functions may support the MP3 format for short music clips that play as ringtones.
  Unlike some formats, MP3 files usually do not include DRM technology that would limit playback and sharing.
  MP3 files can be created at different "bit rates". Higher bit rates offer better sound quality, but also increase file size, requiring more memory space to store.
• Music Player:  The phone includes memory storage for MP3, AAC or similar music files, and software for playing that music. Generally, music can be downloaded into the phone from a computer and played back later through a headset attached to the phone.
  Newer phones with High-Speed Data may support downloading music directly over the mobile network
• OEM: Original Equipment by Manufacturer. 
• OLED:  Organic Light-Emitting Diode. A next-generation display technology that consists of small dots of organic polymer that emit light when charged with electricity. OLED displays are thinner, lighter, brighter, cheaper to manufacture and consume less power than the current LCD displays.
• PDA: Personal Digital Assistant. Example: Palm Treo
• Polyphonic Ring Tones: Polyphonic comes from the word polyphony, meaning "many sounds". Music that has many notes sounding together, either in a chordal, or countrapuntal setting. Polyphonic ringtones vary in specification from phone to phone, but all polyphonic phones support the playing of more than one note together, so your ringtone is generally more musical.
• POP:   Post Office Protocol
  An Internet protocol used to download messages from an email server to an email client (usually email software running on a PC or mobile device).
  POP3 is the most common email-downloading protocol. IMAP is a newer alternative to POP, and there are proprietary protocols as well, such as Outlook/Exchange and BlackBerry.
• Predictive Text Input: A technology which allows you to enter text by pressing only one key per letter. The phone will automatically compare all of the possible letter combinations against a built-in dictionary of words. The current Predictive Text Input implementations are T9, iTAP and eZiText.
• Push to Talk:  PTT is a two-way communication service that works like a "walkie talkie".
• Quad Band: GSM phone that supports all 4 major GSM bands and can be used basically anywhere there is GSM service.
• QWERTY:  QWERTY is a standard layout for letter keys on text keyboards and thumboards. Originally created for typewriters, it is currently the layout found on most English-language computer keyboards. It is named for the order of the first six keys on the top row, which happen to form a pronounceable word
• Refurbished:   Refurbished phones are used phones that have been inspected, tested, and restored to full working condition at a factory or authorized service center. They may feature new housings or other new parts, or they may simply be used phones that have been tested and certified.
• Ringer Profiles:  Ringer Profiles allow the user to create distinct "profiles", each consisting of an array of detailed ringer settings. These profiles can be pre-set and stored in the phone by the user, then quickly selected and activated at any time.
  This feature is useful because many phones offer a very large array of ringer options. Different ringer options, (including tones, melodies, vibrate, flashing lights, or any combination thereof,) may be applied to incoming calls, incoming SMS, service status, incoming Wireless Internet push messages, alarms, etc. In addition, some phones allow different ringers to be used for incoming roaming calls, calls from numbers in the phone book, and even different ringers for individual numbers in the phone book.
  With all of those options, profiles make it easy to create sets of settings that are appropriate for various situations, including work, home, public, etc.
• Roaming: Means that your mobile phone automatically sets up communication procedures with different radio base stations when you are on the move. International roaming means that you can use networks other than your own when traveling abroad. Some phones allow for example switching between 900/1800 in Europe to 1900 in US
• SD: Secure Digital
  A type of removable flash memory card.
  Like any flash memory card, it can be used to store various types of files, including photos, videos, music, or software.
  SD is smaller than Compact Flash, but larger than miniSD, TransFlash, or RS-MMC. SD is the same size as MMC, but thicker. Most devices with SD slots can also accept MMC cards, but not vice-versa.
  SD cards are generally faster than MMC, but use more power.
  There is an extension of the SD protocol known as SDIO that allows devices other than memory cards to be used in SD slots, such as cameras or Wi-fi adapters.
• Service Provider:  Wireless carriers, also called service providers or operators, are the companies that operate the wireless networks and sell use of those networks (the service).
  The network consists of antennas linked to base stations (commonly called "towers"), and infrastructure linking them. The service is simply allowing customers to access the network, typically billed by the minute.
  Some carriers offer flat-rate plans. Still others, called MVNOs, do not own a network.
• SIM Card: Subscriber Identity Module. The smart card used in digital phones. It carries the user's identity for accessing the network and receiving calls and also stores personal information, such as phone directory and received SMS messages.
• Smartphone: A category of mobile device that provides advanced capabilities beyond a typical mobile phone. Smartphones run complete operating system software that provides a standardized interface and platform for application developers.
  By the strict definition, smartphones are distinct from PDA-based devices running operating systems such as Palm OS or Windows Mobile for Pocket PCs. While PDA-based devices usually have a touch-screen for pen input, smartphones usually have a standard phone keypad for input.
  Compared to standard phones, smartphones usually have larger displays and more powerful processors.
  Applications written for a given smartphone platform can usually run on any smartphone with that platform, regardless of manufacturer. Compared to Java or BREW applications, native smartphone applications usually run faster and integrate more tightly with the phone's features and user interface.
  The two major smartphone platforms are Series 60 (by Nokia) and Windows Mobile for Smartphones (by Microsoft).
  Phones that are not smartphones or PDA phones are called Feature Phones
• SMS: The short message service (SMS) enables you to send and receive text messages using your mobile phone or personal communicator. Depending on your network service provider and your plan, you can send messages to other mobile phones or to PCs, domestically or internationally. The cost is usually a low, flat rate or even free, depending on your contract
• Speakerphone: or Build-in Handsfree. Allows the phone to be used at a short distance, without the phone being held next to the face.
• STN:  Super Twisted Nematic. A type of LCD display technology. STN uses less power and is less costly than TFT technology, but at the expense of image quality and response time.
• Symbian: Symbian is a venture formed by Nokia, Ericsson, Motorola, and Psion to create easy to use operating systems for wireless devices and personal digital assistants (PDAs). 
• T9 Input Text: T9 Text Input is software that enables users to easily enter text into small devices with limited size keyboards, like mobile phones. T9 Text Input replaces the traditional "multi-tap" method of entering text providing the ability to enter text using only one keystroke per letter. T9 Text Input gives the phone's standard keypad the capabilities of a full keyboard requiring only one key press per letter. Using the letters on each phone key and a highly compressed database, the T9 software translates key press sequences into words.
• Talk Time: The length of time a wireless device may be engaged in transmission (phone conversations, sending or receiving data) before it runs out of battery power. Talk time, expressed in hours and minutes, is much shorter than standby time because transmission requires more power.
• TDMA: Time Division Multiple Access.  Currently being switched off in the US in favor of GSM or CDMA (depending on carrier)
• TFT: Thin Film Transistor. A type of LCD display technology. Compared to other types of LCD technology, TFT features excellent image quality and response time, but uses more power, and is more expensive
• Touch Screen: Touch-screens are typically found on larger displays, in phones with integrated PDA features. Most are designed to work with either your finger or a special stylus. Tapping a specific point on the display will activate the virtual button or feature displayed at that location on the display.
  Some phones with this feature can also recognize handwriting written on the screen using a stylus, as a way to quickly input lengthy or complex information.
• TransFlash:  A type of removable flash memory card designed specifically for mobile phones.
  Like any flash memory card, it can be used to store various types of files, including photos, videos, music, or software.
  TransFlash cards were introduced on the market in 2004. In 2005, the format morphed into microSD. It is mostly just a name change, as all microSD cards should be compatible with TransFlash slots and vice-versa. However microSD cards can also include functionality such as NFC, when used with a compatible microSD-enabled phone.
  MicroSD / TransFlash are one of the smallest memory card formats available; a microSD / TransFlash card is about the size of a fingernail. It was designed to be smaller than competing formats, to allow phones using the format to be smaller overall.
  Before the first cards reached the market, the format was first introduced as "T-Flash", and before that it was known within the industry as "TriFlash-R". TransFlash was the final name when it reached the market, but that is now changing to microSD.
• Tri Band: A GSM phone that supports three of the four major GSM frequency bands, and will therefore work in most parts of the world.
  There are two major types of tri-band GSM phones: European and Americas.
  European tri-band phones support the 900, 1800, and 1900 frequency bands. They provide complete coverage in Europe, Africa, and Asia, and work on at least one network in most countries in the Americas.
  America's tri-band phones support the 800/850, 1800, and 1900 frequency bands. They provide complete coverage in the Americas, and will work on at least one network in most countries in Europe, Africa, and Asia.
  NOTE: This definition applies to the U.S. and Canada, and may not be accurate for other countries.
• UMTS (Universal Mobile Telecommunications System): The name for the third generation mobile telephone standard in Europe. Also described as 3G.
• WAP: The Wireless Application Protocol is a family of protocols allowing mobile devices to access wireless services. Wireless Application Protocol (WAP) is a global, open standard that gives mobile users access to Internet services through handheld devices. It enables users to easily access a whole range of Mobile Internet and other data services from mobile devices such as smartphones and communicators, and without the need to plug into a separate laptop or data-enabled device.
  WAP enables this through a built-in "WAP microbrowser" that lets information be accessed direct from a phone, in the same way that web browsers provide access to on-line services via an Internet-ready PC. Typically, a WAP screen will display a number of hyperlinks to various services or information portals.
  As well as WAP phones, Ericsson has also announced a WAP Service Developer's Kit (WapIDE) and the WAP Gateway/Proxy, which bridges WAP applications and services in Internet and intranet environments with mobile networks. In addition, Ericsson provides application enablers, such as Ericsson Localized Internet (ELI) for location-based services, and WAP Application Server (WAS) providing a run-time and development environment for WAP applications.
• WCDMA (Wideband Code Division Multiple Access): Universal Mobile Telecommunications System. A third-generation (3G) wireless communications technology and the next generation of GSM. UMTS is a wireless standard approved by the International Telecommunications Union and is intended for advanced wireless communications.
  UMTS uses WCDMA technology, and the two terms are often used interchangeably with each other.
• Unlocked Phone: Although there are several types of "locks" that can apply to a phone, the most talked-about type is a carrier lock, also known as a SIM lock or subsidy lock.
  Many phones sold by carriers come "locked" to that carrier. A "locked" phone can only be used with that carrier; it cannot be used with another carrier's service. (Not counting roaming.).  An unlocked phone can be used with any carrier sim card.
• USB: USB (Universal Serial Bus) is a type of plug-in connection that is used to connect devices, including some phones, to desktop or laptop computers. In a phone, USB is useful for quickly transferring files to and from phones, or for synchronizing address book and calendar information with a computer application such as Outlook.
• Video Calling: Also known as "videophone", or "video conferencing", this feature lets two people with 3G video phones talk to each other while viewing 2-way live video of each other.
  Some phones with this feature have a camera that rotates or swivels, so it can face the user for video calling, and face "out" for taking photos. Other phones have two cameras - one facing in and one facing out.
  This feature requires a 3G network that specifically supports video calling. It will only work when the phone is in range of such a network. Both phones must also support video calling - not all 3G phones do.
• Voice Dial: A feature that allows a user to dial a phone number by spoken commands.
• WCDMA: Wideband Code Division Multiple Access. An approved third-generation (3G) wireless standard which utilizes one 5 MHz channel for both voice and data, offering data speeds of 144 Kbps to 2 Mbps.  (WCDMA and UMTS are often used interchangeably.)
• WIFI: Wi-Fi® is a WLAN (Wireless Local Area Network) technology. It primarily provides short-range wireless high-speed data connections between mobile data devices (such as laptops) and nearby Wi-Fi access points (special hardware connected to a wired network).
  Wi-Fi is a trademark of the Wi-Fi Alliance, a nonprofit industry association. The IEEE technical specification for Wi-Fi is 802.11.
  There are several variants of 802.11. The most common is 802.11b, which provides speeds up to 11 Mbps. 802.11g and 802.a are faster versions. Many 802.11g and 802.11a products are backward-compatible with the original 802.11b.
  Wi-Fi is generally much faster than data technologies operating over the cellular network like GPRS, EDGE, 1xRTT, HSDPA, and EV-DO.
  It is much shorter-range, however. Wi-Fi coverage is only provided in small, specific areas called "hot spots". Other than some corporate or educational campuses, Wi-Fi coverage is not widespread. Range for a typical Wi-Fi base station (access point) is typically around 100 to 300 feet indoors and 2000 feet outdoors.
  Most Wi-Fi operates in the 2.4 GHz unlicensed frequency band. This is the same band as Bluetooth and some cordless phones, although the technologies are designed to co-exist and not interfere. 802.11a operates in the 5 GHz unlicensed frequency band.

Wi-Fi networks can be set up and operated by anyone, with different networks allowing different kinds of access. A public "hot spot" at an airport or coffee shop might charge an hourly rate for access. A hotel might offer free wi-fi to guests. A company or university might offer on-premises free access for verified employees/students. Or a home user could set up their own network to which only they had access.
While most Wi-Fi connections are between a mobile device and an access point, it is also possible to create an "ad-hoc" network directly among two or more devices, without an access point.