Area code

The area code is a part of a telephone number normally occurring at the beginning of the number, that usually indicates a geographical area. It directs telephone calls to particular regions on a public switched telephone network (PSTN), where they are further routed by the local network.

Callers within the geographical area of a given area code usually do not need to include this particular area code in the number dialed, thereby giving the caller shorter local telephone numbers. In international phone numbers, the area code directly follows the country calling code.

While the E.164 standard regulates country codes at the international level, it is each country's responsibility to define the numbering within its own network. As a result, area codes may have:

• A fixed length, e.g. 3 digits in the US; 2 digits in Australia.
• A variable length, e.g. between 2 and 5 in Germany and in Austria; between 1 and 3 in Japan.
• Or be incorporated into the subscriber's number, as is the case in many countries, such as Spain or Norway. This is known as a "closed" telephone numbering plan. In some cases a trunk code (usually 0) must still be dialled, as in Belgium, Switzerland and South Africa.

In many cases the area codes determine the rate (price) of a call. For example, in North America calls to the 800, 888, 877, and 866 areas are free to the caller and paid by the receiver, while calls to the 900 area are "premium rate", which means "very expensive". Normally intra-area calls are charged lower than inter-area calls, but there are exceptions, e.g. in Israel both are charged at the same rate.

United States and Canada

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, and was extended to [2-9][0-8][0-9]-[2-9][0-9][0-9] (referred to as NPA-NXX). "X11" combinations (such as 911) are not eligible to be used as area codes.

Not all area codes correspond to a 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, although such services also exist in some places on a local basis using a particular three-digit prefix following the area code, often "976"). Area code 710 has been reserved for the United States Government, although no lines - other than the single telephone number 710-627-4387 ("NCS-GETS") - had actually been connected on this code as of 2004.

None of these changes enable the existence of variable length area codes, which are commonplace outside North America. Also see [1].

There are several noteworthy peculiarities in the NANP:

• In some localities you need to dial the area code even when calling within the same area; this is usually the case in urban areas where a 'local' call may be in another area code, or where two different area codes are overlaid on the same geographical area. In most cases a "1" needs to be dialed before the area code as well.
• Mobile phones are allocated numbers within regular geographic area codes corresponding (usually) to the subscriber's home or work location, instead of within a distinctive subset of area codes (e.g. 07xxx in the UK).
  Since a calling party cannot reliably distinguish between landline and mobile phone numbers, this forced NANP cellular telephone carriers into a charging model wherein the cellular subscriber usually pays for all airtime on his/her phone, whether placing or receiving a call, as opposed to the distinctive-subset model in which callers are usually charged at a higher rate ("caller-pays") for dialing mobile numbers than landlines. Some have cited this "receiver-pays" model as a reason for the US's relatively slow adoption rate of cellular telephony in the 1990s, compared to that in Europe and the Pacific Rim, though this has been largely countered by the post-2000 prevalence of free long-distance calling (to cellular or landline phones) on nearly all US cellular plans.

See also: List of North American area codes.

Another oddity of NANP telephone numbering is the popularity of alphabetic dialing. On most US telephones, three letters appear on each number button from 2 through 9. This accommodates 24 letters. Historically, the letters Q and Z were omitted, though on some modern telephones, they are added, so that the alphabet is apportioned as follows:

2 = ABC
3 = DEF
4 = GHI
5 = JKL
6 = MNO
7 = P(Q)RS
8 = TUV
9 = WXY(Z)

No letters are allocated to the 1 or 0 keys (although some corporate voice mail systems are set up to count Q and Z as 1, and some old telephones assigned the Z to the digit 0).

Originally, this scheme was meant as a mnemonic device for telephone number prefixes. When telephone numbers in the US were standardized in the mid-20th century, they were made seven digits long, including a 2-digit prefix, the latter expressed as letters rather than numbers (before World War II many localities used three letters and four numbers, and in much of California during this period phone numbers had only six digits - two letters followed by four numbers). The prefix was a name, and the first two or three letters (usually shown in capitals) of the name were dialed. After World War II, the third letter (where previously used) was replaced by a number (although New York City did this in 1930). Thus, the famous Glenn Miller tune "PEnnsylvania 6-5000" refers to a telephone number that would have been dialed 736-5000 (when the song came out in 1940, this was the number of the Hotel Pennsylvania, located across the street from the present Madison Square Garden; the hotel has changed ownership several times since then but still bears the same number today). Similarly, the classic Elizabeth Taylor film "BUtterfield 8" refers to the section of New York City where the film is set, where the telephone prefixes include 288 (on the East Side of Manhattan between roughly 64th and 86th Streets). This author's childhood telephone number was MOhawk 5-6612.

Today this system has been abandoned, but alphabetic dialing remains as a commercial mnemonic gimmick, particularly when combined with toll-free numbers. For example, one can dial 1-800-FLOWERS to send flowers to someone. Sometimes, longer words are used - for example one might be invited to give money to a public radio station by dialing 1-866-KPBS-GIVE. The "number" is 8 digits long, but only the first seven need be dialed. If an eighth (or more) digit is dialed, the switching system will ignore it.

United Kingdom

In the United Kingdom, area codes are -- including the leading '0' which is dropped when calling UK numbers from overseas --three or four or five digits long, with larger towns and cities having shorter area codes permitting a larger number of telephone numbers in the ten digits used. Area codes are sometimes still called STD (Subscriber Trunk Dialling) codes.

A short list of examples, set out in the officially approved (Ofcom) number groups:

• 020 xxxx xxxx: London
• 028 xxxx xxxx: Northern Ireland
• 029 xxxx xxxx: Cardiff
• 0131 xxx xxxx: Edinburgh
• 01382 xxx xxx: Dundee, a typical area code

See UK Telephone Numbering Plan.

Netherlands

(see also Communications_in_the_Netherlands#Area_codes and the next section of that article)

In the Netherlands, the area codes are -- excluding the leading '0' -- one, two or three digits long, with larger towns and cities having shorter area codes permitting a larger number of telephone numbers in the ten digits used.

• (0)10 : Rotterdam
• (0)20 : Amsterdam
• (0)30 : Utrecht
• (0)40 : Eindhoven
• (0)50 : Groningen
• (0)6 : mobile phone number
• (0)676 : internet access phone number
• (0)70 : The Hague
• (0)800 : toll free number
• (0)900 : premium rate call
• (0)906 : premium rate
• 112 : emergency phone number

See also

• Telephone numbering plan regarding numbering plans in different countries.
• North American Numbering Plan for more details regarding area codes in the US and elsewhere in North America.

External links

• World Telephone Numbering Guide
• Free Area Code Listing (US and Canada)
• North American Numbering Plan Administration (NANPA)