Telephone area code

The area code is a part of a telephone number normally occurring at the beginning that usually indicates a geographical area. Callers within the geographical area of a given area code, usually do not need to include this particular area code in the number dialled, thereby availing the caller short local telephone numbers.

In the United States and Canada, area codes are regulated by the North American Numbering Plan. Currently, all area codes in the NANP must have 3 digits. Many other countries have area codes that are shorter for heavily populated areas and longer for lightly populated areas. Area codes are also referred to as NPAs, for Numbering Plan Area.

Before 1995, North American area codes were of the form [2-9][0/1][0-9], with the prefix or NNX in the form [2-9][2-9][0-9]; that codespace filled up due to overallocation of , and was extended to [2-9][0-8][0-9]-[2-9][0-9][0-9] (referred to as NPA-NXX).

Not all area codes correspond to geographical area. Codes 8xx with the last two digits matching, such as 800, 888, 877, 866, etc. are reserved for toll free calls. Code 900 is reserved for premium-rate calls (also known as dial-it services).

There are a number of proposals for what the NANP should do when this larger space fills up. In one proposal, existing codes may be changed to "a9bc" (e.g. San Francisco 415 would become 4915); once that conversion is complete, the new second digit would be opened for a new range. Other proposals include reallocating blocks of numbers assigned to smaller long distance carriers or unused reserved services. None(?) of these changes enable the existence of variable length area codes, which are common place outside the USA (See United Kingdom below). Also see ["http://www.lincmad.com/whynot8"]

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In the United Kingdom, area codes are -- excluding the leading '0' -- two, three or four digits long, with larger towns and cities having shorter area codes permitting a larger number of telephone numbers in the ten digits used. London was exceptional, having two area codes, '171' and '181', although this has now been changed. Until recently, the first digit was always '1', but with the growth in telephone use '2' is now used for certain areas. Where the first digit is '5-9' this designates special numbers (toll free, mobile telephones, etc), while digits 3 and 4 are reserved for future use. A short list of examples:

• (0) 20 xxxx xxxx: London
• (0) 131 xxx xxxx: Edinburgh
• (0) 1382 xxx xxx: Dundee, a typical area code

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see also country calling codes, Telephone number