Mobile Phone

Cordless telephone linked to a cellular radio network. Early cellular networks used analogue technology, but since the late 1990s most services use a digital system. Calls are linked to the public telephone system via a network of connected base stations and exchanges; the area covered by each base station is called a cell. Each cell is about 5 km/3 mi across, and has a separate low-power transmitter. Mobility is possible as calls can be made while moving from one radio cell to another. In Europe, GSM (Global System for Mobile communications) has been adopted by many countries as a digital standard, enabling travellers to use a single phone across different national networks. Tri-band mobile phones are capable of changing frequencies to allow local networks in the USA to be accessed.

A trend for greater integration of phone and computer led to the development of WAP (wireless application protocol) phones in 1999. These allowed users to read e-mails and browse the Web, and by 2002 users could send digital images using a built-in digital camera. High-speed, ‘third generation’ (3G) phones were launched, capable of sending and receiving video messages, video calling, e-mail, photo-messaging, and news and information services (see 3G). Other potential applications include interactive television and all the features of a personal digital assistant (PDA).

Mobile phone services rely on an internal Subscriber Identity Module (SIM) card. The SIM card identifies the phone to its network, can store telephone numbers, and protects users against misuse of their network account. Most mobile phone services offer a service called SMS messaging, which allows users to send each other text messages. GPRS (General Packet Radio Services) allows users to have their mobile phones permanently connected to the Internet.