Call screening
Facility on some answering machines that allows the user to hear who’s calling so they can decide whether to answer in person or not.

CDMA
Code Division Multiple Access: Digital cellular standard used in Japan, parts of the Far East and parts of the USA. Uses coding of digital segments of calls to enable them to use vacant channels over a broad range of frequencies.

Cell broadcast
Service provided by digital cellphone networks where useful info is provided to users via on-screen text messages. Currently used by Vodafone and BT Cellnet to inform customers of the STD code of the area they are currently located – enabling them to take full advantage of local call discount schemes.

Cellular
A radio phone system in which a network of transmitters links the mobile user to the public phone system. Each transmitter covers users in its own ‘cell’.

CLI
Calling Line Identification. A range of services in which the number of a caller can be accessed by the recipient. The 1471 service offered free to BT customers is one of these – as is the caller display service provided to digital cellphone users.

Clone
Whereby a ‘cloned’ analogue cellphone is illegally re-chipped with an ESN belonging to another. Can also refer to a phone ‘badged’ by one company and sourced from another.

Coverage
The area in which a cellphone can make or receive calls. Coverage is usually expressed by networks as a percentage of the resident population who could use mobiles outside their own homes. Geographic coverage, therefore, is far inferior to this ‘by population’ figure.

CT0
The standard used by first-generation cordless phones. This analogue system can make use of just eight channels (some phones use only one), which can lead to problems with interference, particularly in built-up areas.