Editing Telephone numbering plan (section)

===Area code<span class="anchor" id="area code"></span>===
{{redirects here|Area code|the songs|Area Codes (Ludacris song)|and|Area Codes (Kali song)}}
Telephone administrations that manage telecommunication infrastructure of extended size, such as a large country, often divide the territory into geographic areas. This benefits independent management by administrative or historical subdivisions, such as states and provinces, of the territory or country.  Each area of subdivision is identified in the numbering plan with a routing code. This concept was first developed in the planning for a ''nationwide numbering plan'' for [[Operator Toll Dialing]] and [[direct distance dialing]] (DDD) in the Bell System in the United States in the 1940s, a system that resulted in the [[North American Numbering Plan]] for World Zone 1.<ref>{{cite journal |first1=J.J. |last1=Pilliod |first2=H.L. |last2=Ryan |url=https://archive.org/details/sim_bell-telephone-magazine_summer-1945_24_2/page/n50/ |title=Operator Toll Dialing—A New Long Distance Method |journal=Bell Telephone Magazine |volume=24 |pages=101–115 |date=Summer 1945}}</ref> AT&T divided the United States and Canada into [[numbering plan area]]s (NPAs), and assigned to each NPA a unique three-digit prefix, the ''numbering plan area code'', which became known in short-form as ''NPA code'' or simply area code. The area code is prefixed to each telephone number issued in its service area.

Other national telecommunication authorities use various formats and dialing rules for area codes. The size of area code prefixes may either be fixed or variable. Area codes in the NANP have three digits and two digits are used in [[Communications in Brazil|Brazil]], one digit in [[Telephone numbers in Australia|Australia]] and [[Telephone numbers in New Zealand|New Zealand]]. Variable-length formats exist in many countries including [[Telephone numbers in Argentina|Argentina]], [[Telephone numbers in Austria|Austria]], [[Telephone numbers in Germany|Germany]], [[Telephone numbers in Japan|Japan]], [[Telephone numbers in Mexico|Mexico]], and the [[Telephone numbers in the United Kingdom|United Kingdom]].

In addition to digit count, the format may be restricted to certain digit patterns. For example, the NANP had at times specific restrictions on the range of digits for the three positions, and required assignment to geographical areas avoiding nearby areas receiving similar area codes to avoid confusion and misdialing.

Some countries, such as [[Telephone numbers in Denmark|Denmark]] and [[Telephone numbers in Uruguay|Uruguay]], have merged variable-length area codes and telephone numbers into fixed-length numbers that must always be dialed independently of location. In such administrations, the area code is not distinguished formally in the telephone number.

In the UK, area codes were first known as [[subscriber trunk dialling]] (STD) codes. Depending on local dialing plans, they are often necessary only when dialed from outside the code area or from mobile phones.  In North America, [[ten-digit dialing]] is required in areas with [[overlay complex|overlay numbering plans]], in which multiple area codes are assigned to the same area.

The strict correlation of a telephone number to a geographical area has been broken by technical advances, such as [[local number portability]] in the North American Numbering Plan and [[voice over IP]] services.<ref>{{Cite news
 |first=Amy|last=Saunders
 |title=Cell-phone age turns the 614 into just numbers
 |date=2009-05-16
 |access-date=2009-08-21
 |work=[[The Columbus Dispatch]]
 |url=http://www.dispatch.com/live/content/local_news/stories/2009/05/16/0_AREA_CODES.ART_ART_05-16-09_A1_5JDSM84.html
 |url-status=dead
 |archive-url=https://web.archive.org/web/20100323035022/http://www.dispatch.com/live/content/local_news/stories/2009/05/16/0_AREA_CODES.ART_ART_05-16-09_A1_5JDSM84.html
 |archive-date=2010-03-23
}}</ref>

When dialing a telephone number, the area code may have to be preceded by a [[trunk prefix]] or national access code for domestic calls, and for international calls by the international access code and country code.

Area codes are often quoted by including the national access code. For example, a number in [[London]] may be listed as ''020 7946 0321''. Users must correctly interpret ''020'' as the code for London. If they call from another station within London, they may merely dial ''7946 0321'', or if dialing from another country, the initial ''0'' should be omitted after the country code.