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A mobile or cellular telephone is a long-range, portable electronic device for personal telecommunications over long distances. In addition to the standard voice function of a telephone, current mobile phones can support many additional services such as SMS for text messaging, email, packet switching for access to the Internet, and MMS for sending and receiving photos and video. Most current mobile phones connect to a cellular network of base stations (cell sites), which is in turn interconnected to the public switched telephone network (PSTN) (the exception are satellite phones).

Mobile phones are distinct from cordless telephones, which generally operate only within a limited range of a specific base station. Technically, the term mobile phone includes such devices as satellite phones and pre-cellular mobile phones such as those operating via MTS which do not have a cellular network, whereas the related term cell(ular) phone does not. In practice, the two terms are used nearly interchangeably.

Invented in 1997, the camera phone is now 85% of the market. In a recent Weekend America interview on public radio, Philippe Kahn, the inventor of the camera phone, discusses its social impact and how it connects people around the world [3]. Mobile phones also often have features beyond sending text messages and making voice calls—including Internet browsing, music (MP3) playback, memo recording, personal organizers, e-mail, built-in cameras and camcorders, ringtones, games, radio, Push-to-Talk (PTT), infrared and Bluetooth connectivity, call registers, ability to watch streaming video or download video for later viewing, video call and serve as a wireless modem for a PC.

In most countries, including Europe, Japan, Pakistan, Australia, India[12], Maldives and Israel the person receiving a mobile phone call pays nothing. However, in Hong Kong, Canada, and the United States, one can be charged per minute. In the United States, a few carriers are beginning to offer unlimited received phone calls. For example as of December 2006, Sprint now has 4 plans under "Sprint Free Incoming Plans" section of their website, although the restriction is the receiving phone must be on the Sprint PCS network. For the Chinese mainland, it was reported that both of its two operators will adopt the caller-pays approach as early as January 2007.[12] However it is getting to the point where a mobile phone will become more like a Portable Media Device and less like a mobile phone. This is due to it being able to play, music, videos and games as well as show pictures send text messages and phone people, access the internet and send files.

Mobile phones and the network they operate under vary significantly from provider to provider, and nation to nation. However, all of them communicate through electromagnetic microwaves with a cell site base station, the antennas of which are usually mounted on a tower, pole, or building.

The phones have a low-power transceiver that transmits voice and data to the nearest cell sites, usually 5 to 8 miles (approximately 8 to 13 kilometres) away. When the mobile phone or data device is turned on, it registers with the mobile telephone exchange, or switch, with its unique identifiers, and will then be alerted by the mobile switch when there is an incoming telephone call. The handset constantly listens for the strongest signal being received from the surrounding base stations. As the user moves around the network, the mobile device will "handoff" to various cell sites during calls, or while waiting (idle) between calls it will reselect cell sites.

Cell sites have relatively low-power (often only one or two watts) radio transmitters which broadcast their presence and relay communications between the mobile handsets and the switch. The switch in turn connects the call to another subscriber of the same wireless service provider or to the public telephone network, which includes the networks of other wireless carriers. Many of these sites are camouflaged to blend with existing environments, particularly in high-scenery areas.

The dialogue between the handset and the cell site is a stream of digital data that includes digitized audio (except for the first generation analog networks). The technology that achieves this depends on the system which the mobile phone operator has adopted. Some technologies include AMPS for analog, and D-AMPS, CDMA2000, GSM, GPRS, EV-DO, and UMTS for digital communications. Each network operator has a unique radio frequency band.