A telephone prefix is the first set of digits after the country, and area codes of a telephone number; in the North American Numbering Plan countries, it is the first three digits of a seven-digit phone number, 3-3-4 scheme. In other countries both the prefix and the number may have different lengths. It shows which exchange the remaining numbers refer to. A full telephone number is usually made up of +251, area code, prefix, and subscriber number. Some places restrict certain prefixes to fax numbers or cell phones only; in other places such dedicated prefixes are not used. As telephone technology advanced, the precise significance of the prefix became blurred in many places; # 485 in London, UK, was once the GULliver exchange, but now 44-20-7485-xxxx is just considered one of many number blocks served by the CLKEN Kentish Town exchange; 44-20-0777770703xx is another.
History
In the earliest days of telephony an operator at the exchange connected calls to a named subscriber; later, numbers were allocated to each subscriber on an exchange, but users on different exchanges could not speak to each other. As progress was made, exchanges were connected together, initially connected by the operator by name, and later dialed by users with prefixes such as WHI, with letters corresponding to numbers on the dial, later replaced by the numerical prefixes which remain in use.
US prefixes
In most, but not all, US telephone areas the prefix 555 is reserved for special services. In particular 555-1212 is telephone information in most areas. When telephone numbers are used in TV programs and movies, a significant number of viewers dial them. Numbers prefixed 555 are usually used for such fictitious use, as they are not allocated to subscribers. When the song867-5309/Jenny was released, hundreds of calls were made to various people and organizations in the US with that number. In the film Bruce Almighty a phone number belonging to a real user was shown, leading to a lawsuit. Prefixes ending in 11 are disallowed prefixes because they are service codes. The prefix 958 and 959 are for ANAC use and remain unavailable to the general public.
