Editing Telephone numbering plan (section)

==Telephone number structure==
National or regional telecommunication administrations that are members of the [[International Telecommunication Union]] (ITU) use national telephone numbering plans that conform to international standard [[E.164]].

E.164 specifies that a telephone number consist of a country code and a national telephone number. National telephone numbers are defined by national or regional numbering plans, such as the [[European Telephony Numbering Space]], the [[North American Numbering Plan]] (NANP), or the [[telephone numbers in the United Kingdom|UK number plan]].

Within a national numbering plan, a complete destination telephone number is typically composed of an area code and a subscriber telephone number.

Many national numbering plans have developed from local historical requirements and progress or technological advancements, which resulted in a variety of structural characteristics of the telephone numbers assigned to telephones. In the United States, the industry decided in 1947 to unite all local telephone networks under one common numbering plan with a fixed length of ten digits for the national telephone number of each telephone, of which the last seven digits were known as the local ''directory number'', or ''subscriber number''. Such a numbering plan became known as a closed numbering plan.<ref name="notes1980">{{cite book|publisher=AT&T |title=Notes on the Network |section= 10-3.02: INTERNATIONAL DIRECT DISTANCE DIAUNG (IDDD) |page=3 |year=1980 |url=http://historyofphonephreaking.org/docs/notn1980.pdf}}</ref> In several European countries, a different strategy prevailed, known as the open numbering plan, which features a variance in the length of the area code, the local number, or both.<ref name="myers1961">{{cite journal |first1=O. |last1=Myers |first2=C. A. |last2=Dahlbom |title=Overseas Dialing: A Step Toward Worldwide Communication |journal=Telephone Engineer & Management |volume=65 |issue=22 |date=1961-11-15 |pages=46–49}}</ref>

[[File:Nixoncard.jpg|thumb|United States telephone numbers often included letter prefixes and [[telephone exchange names]], which were more easily memorable for users than long digit sequences.]]

===Subscriber number===
The subscriber number is the address assigned to a telephone line or wireless communication channel terminating at the customer equipment. The first few digits of the subscriber number may indicate smaller geographical scopes, such as towns or districts, based on municipal aspects, or individual [[telephone exchange]]s (''central office code''), such as a wire centers. In mobile networks they may indicate the network provider. Callers in a given area sometimes do not need to include area prefixes when dialing within the same area, but devices that dial telephone numbers automatically may include the full number with area and access codes.

The subscriber number is typically listed in local telephone directories, and is therefore often referred to as the ''directory number''.

===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.