A telephone numbering plan is a type of numbering scheme used in telecommunication to assign telephone numbers to subscriber telephones or other telephony endpoints. Telephone numbers are the addresses of participants in a telephone network, reachable by a system of destination code routing. Telephone numbering plans are defined in each of administrative regions of the public switched telephone network (PSTN) and they are also present in private telephone networks. For public number systems, geographic location plays a role in the sequence of numbers assigned to each telephone subscriber.
Numbering plans may follow a variety of design strategies which have often arisen from the historical evolution of individual telephone networks and local requirements. A broad division is commonly recognized, distinguishing open numbering plans and closed numbering plans. Many numbering plans subdivide their territory of service into geographic regions designated by a prefix, often called an area code or city code, which is a set of digits forming the most-significant part of the dialing sequence to reach a telephone subscriber.
The International Telecommunication Union (ITU) has established a comprehensive numbering plan, designated E.164, for uniform interoperability of the networks of its member state or regional administrations. It is an open numbering plan, however, imposing a maximum length of 15 digits to telephone numbers. The standard defines a country calling code (country code) for each state or region which is prefixed to each national numbering plan telephone number for international destination routing.
Private numbering plans exist in telephone networks that are privately operated in an enterprise or organizational campus. Such systems may be supported by a private branch exchange (PBX), which provides a central access point to the PSTN and also controls internal calls between telephone extensions.
In contrast to numbering plans, which determine telephone numbers assigned to subscriber stations, dialing plans establish the customer dialing procedures, i.e. the sequence of digits required to reach a destination. Even in closed numbering plans, it is not always necessary to dial all digits of a number. For example, an area code may often be omitted when the destination is in the same area as the calling station.
Most national telephone administrations have enacted numbering plans that conform to the international standard E.164. E.164 conformant telephone numbers consist of a country calling 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 UK number plan.
Within the national numbering plan, a complete destination telephone number is composed of an area code and a subscriber telephone number. The subscriber number is the number assigned to a line connected to customer equipment. The first few digits of the subscriber number may indicate smaller geographical areas or individual telephone exchanges. In mobile networks they may indicate the network provider. Callers in a given area or country sometimes do not need to include the particular area prefixes when dialing within the same area. Devices that dial telephone numbers automatically may include the full number with area and access codes.
Country codes are necessary only when dialing telephone numbers in other countries than the originating telephone. These are dialed before the national telephone number. By convention, international telephone numbers are indicated in listings by prefixing the country code with a plus sign (+). This reminds the subscriber to dial the international dialing prefix in the country from which the call is placed. For example, the international dialing prefix or access code in all NANP countries is 011, while it is 00 in most European countries. In some GSM networks, it may be possible to dial +, which may be recognized automatically by the network carrier in place of the international access code.
Many telephone numbering plans are structured based on divisions into geographic areas of the service territory. Each area identified in the plan is assigned a numeric routing code. This concept was first developed for Operator Toll Dialing of the Bell System in the early 1940s, which preceded the North American Numbering Plan of 1947. The North American Numbering Plan (NANP) divided the North American service territories into numbering plan areas (NPAs), and assigned to each NPA a unique numerical prefix, the numbering plan area code, which became known in short-form as area code. The area code is prefixed to each telephone number issued in its service area.
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, while two digits are used in Brazil, one digit in Australia and New Zealand. Variable-length formats exist in multiple countries including: Argentina, Austria (1 to 4), Germany (2 to 5 digits), Japan (1 to 5), Mexico (2 or 3 digits), Peru (1 or 2), Syria (1 or 2) and the 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 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 plans.
When dialing a telephone number, the area code may be preceded by a trunk prefix (national access code), 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.
A dial plan establishes the expected sequence of digits dialed on subscriber premises equipment, such as telephones, in private branch exchange (PBX) systems, or in other telephone switches to effect access to the telephone networks for the routing of telephone calls, or to effect or activate specific service features by the local telephone company, such as 311 or 411 service.
A variety of dial plans may exist within a numbering plan and these often depend on the network architecture of the local telephone operating company.
Within the North American Numbering Plan (NANP), the administration defines standard and permissive dialing plans, specifying the number of mandatory digits to be dialed for local calls within the area code, as well as alternate, optional sequences, such as adding the prefix 1 before the telephone number.
Despite the closed numbering plan in the NANP, different dialing procedures exist in many of the territories for local and long distance telephone calls. This means that to call another number within the same city or area, callers need to dial only a subset of the full telephone number. For example, in the NANP, only the 7-digit number may need to be dialed, but for calls outside the local numbering plan area, the full number including the area code is required. In these situations, ITU-T Recommendation E.123 suggests to list the area code in parentheses, signifying that in some cases the area code is optional or may not be required.
Internationally, an area code is typically prefixed by a domestic trunk access code (usually 0) when dialing from inside a country, but is not necessary when calling from other countries; there are exceptions, such as for Italian land lines.
To call a number in Sydney, Australia, for example:
The plus character (+) in the markup signifies that the following digits are the country code, in this case 61. Some phones, especially mobile telephones, allow the + to be entered directly. For other devices the user must replace the + with the international access code for their current location.
New Zealand has a special-case dial plan. While most nations require the area code to be dialed only if it is different, in New Zealand, one needs to dial the area code if the phone is outside the local calling area. For example, the town of Waikouaiti is in the Dunedin City Council jurisdiction, and has phone numbers (03) 465 7xxx. To call the city council in central Dunedin (03) 477 4000, residents must dial the number in full including the area code even though the area code is the same, as Waikouaiti and Dunedin lie in different local calling areas (Palmerston and Dunedin, respectively.)
In the United States, Canada, and other countries or territories using the North American Numbering Plan (NANP), the international trunk access code is 1, which is also the country calling code. The same rule also applies in many parts of the NANP, including all areas of Canada that still have variable-length dial plan. This is not universal, as there are locations within the United States that allow long distance calls within the same area code to be dialed as seven digits. In Canada, the domestic trunk code (long distance access code) must also be dialed along with the area code for long distance calls even within the same area code. For example, to call a number in Regina in area code 306 (Regina and the rest of the province of Saskatchewan are also served by the overlay code 639):
In many parts of North America, especially where a new area code overlays an older area code, dialing the area code, or 1 and the area code, is required even for local calls. Dialing from mobile phones is different in the U.S., as the trunk code is not necessary, although it is still necessary for calling all long distance numbers from a mobile phone in Canada. Most mobile phones can be configured to automatically add a frequently called area code as a prefix, allowing calls within the desired area to be dialed by the user as seven-digit numbers, though sent by the phone as ten-digit numbers.
In some parts of the United States, especially northeastern states such as Pennsylvania served by Verizon Communications, the ten-digit number must be dialed. If the call is not local, the call fails unless the dialed number is preceded by digit 1. Thus:
In California and New York, because of the existence of both overlay area codes (where an area code must be dialed for every call) and non-overlay area codes (where an area code is dialed only for calls outside the subscriber's home area code), "permissive home area code dialing" of 1 + the area code within the same area code, even if no area code is required, has been permitted since the mid-2000s. For example, in the 559 area code (a non-overlay area code), calls may be dialed as 7 digits (XXX-XXXX) or 1-559 + 7 digits. The manner in which a call is dialed does not affect the billing of the call. This "permissive home area code dialing" helps maintain uniformity and eliminates confusion given the different types of area code relief that has made California the nation's most "area code" intensive State. Unlike other states with overlay area codes (Texas, Maryland, Florida and Pennsylvania and others), the California Public Utilities Commission and the New York State Public Service Commission maintain two different dial plans: Landlines must dial 1 + area code whenever an Area Code is part of the dialed digits while cellphone users can omit the "1" and just dial 10 digits.
Many organizations have private branch exchange systems which permit dialing the access digit(s) for an outside line (usually 9 or 8), a "1" and finally the local area code and xxx xxxx in areas without overlays. This aspect is unintentionally helpful for employees who reside in one area code and work in an area code with one, two, or three adjacent area codes. 1+ dialing to any area code by an employee can be done quickly, with all exceptions processed by the private branch exchange and passed onto the public switched telephone network.
In small countries or areas, the full telephone number is used for all calls, even in the same area. This has traditionally been the case in small countries and territories where area codes have not been required. However, there has been a trend in many countries towards making all numbers a standard length, and incorporating the area code into the subscriber's number. This usually makes the use of a trunk code obsolete. For example, to call someone in Oslo in Norway before 1992, it was necessary to dial:
After 1992, this changed to a closed eight-digit numbering plan, e.g.:
while some, like Italy, require the initial zero to be dialed, even for calls from outside the country, e.g.,
While dialing of full national numbers takes longer than a local number without the area code, the increased use of phones that can store numbers means that this is of decreasing importance. It also makes it easier to display numbers in the international format, as no trunk code is required—hence a number in Prague, Czech Republic, can now be displayed as:
as opposed to before September 21, 2002:
Some countries already switched, but trunk prefix re-added with the closed dialing plan, for example in Bangkok, Thailand before 1997:
This was changed in 1997:
Trunk prefix was re-added in 2001
The E.164 standard of the International Telecommunications Union is an international numbering plan and establishes a country calling code (country code) for each member organization. Country codes are prefixes to national telephone numbers that denote call routing to the network of a subordinate number plan administration, typically a country, or group of countries with a uniform numbering plan, such as the NANP. E.164 permits a maximum length of 15 digits for the complete international phone number consisting of the country code, the national routing code (area code), and the subscriber number. E.164 does not define regional numbering plans, however, it does provide recommendations for new implementations and uniform representation of all telephone numbers.
Within the system of country calling codes, the ITU has defined certain prefixes for special services and assigns such codes for independent international networks, such as satellite systems, spanning beyond the scope of regional authorities.
Satellite phones are usually issued with numbers with a special country calling code. For example, Inmarsat satellite phones are issued with code +870, while Global Mobile Satellite System providers, such as Iridium, issue numbers in country code +881 ("Global Mobile Satellite System") or +882 ("International Networks"). Some satellite phones are issued with ordinary phone numbers, such as Globalstar satellite phones issued with NANP telephone numbers.
Some country calling codes are issued for special services, or for international/inter regional zones.
The numbering plan indicator (NPI) is a number which is defined in the ITU standard Q.713, paragraph 18.104.22.168.3, indicating the numbering plan of the attached telephone number. NPIs can be found in Signalling Connection Control Part (SCCP) and short message service (SMS) messages. As of 2004, the following numbering plans and their respective numbering plan indicator values have been defined:
|5||maritime mobile||E.210 and E.211|
Like a public telecommunications network, a private telephone network in an enterprise or within an organizational campus may implement a private numbering plan for the installed base of telephones for internal communication. Such networks operate a private switching system or a private branch exchange (PBX) within the network. The internal numbers assigned are often called extension numbers, as the internal numbering plan extends an official, published main access number for the entire network. A caller from within the network only dials the extension number assigned to another internal destination telephone.
A private numbering plan provides the convenience of mapping station telephone numbers to other commonly used numbering schemes in an enterprise. For example, station numbers may be assigned as the room number of a hotel or hospital. Station numbers may also be strategically mapped to certain keywords composed from the letters on the telephone dial, such as 4357 (help) to reach a help desk.
The internal number assignments may be independent of any direct inward dialing (DID) services provided by external telecommunication vendors. For numbers without DID access, the internal switch relays externally originated calls via an operator, an automated attendant or an electronic interactive voice response system. Telephone numbers for users within such systems are often published by suffixing the official telephone number with the extension number, e.g., 1-800-555-0001 x2055.
Some systems may automatically map a large block of DID numbers (differing only in a trailing sequence of digits) to a corresponding block of individual internal stations, allowing each of them to be reached directly from the public switched telephone network. In some of these cases, a special shorter dial-in number can be used to reach an operator who can be asked for general information, e.g. help looking up or connecting to internal numbers. For example, individual extensions at Universität des Saarlandes can be dialed directly from outside via their four-digit internal extension +49-681-302-xxxx, whereas the university's official main number is +49-681-302-0 (49 is the country code for Germany, 681 is the area code for Saarbrücken, 302 the prefix for the university).
Callers within a private numbering plan often dial a trunk prefix to reach a national or international destination (outside line) or to access a leased line (or tie-line) to another location within the same enterprise. A large manufacturer with factories and offices in multiple cities may use a prefix (such as '8') followed by an internal routing code to indicate a city or location, then an individual four- or five-digit extension number at the destination site. A common trunk prefix for an outside line on North American systems is the digit 9, followed by the outside destination number.
There are many different numbering schemes for assigning nominal numbers to entities. These generally require an agreed set of rules, or a central coordinator. The schemes can be considered to be examples of a primary key of a database management system table, whose table definitions require a database design.
The simplest numbering scheme is to assign cardinal numbers to entities. In some cases (such as computing, time-telling, and in some countries the numbering of floors in buildings) zero-based numbering is used, where the first entity is assigned "zero" instead of "one".
Other numbering schemes are listed by field below.Telephone numbers in Africa
The following are country calling codes in Africa.
Ethiopia (+251)Telephone numbers in Argentina
In Argentina, area codes are two, three, or four digits long (after the initial zero). Local customer numbers are six to eight figures long. The total number of digits is ten, for example, phone number (11) 1234-5678 for Buenos Aires is made up of a 2-digit area code number and an 8-digit subscriber's number, while (383) 123-4567 would be an example of a Catamarca number.Telephone numbers in Asia
Telephone numbers in Asia have the most possible prefixes of any continent on Earth: 2, 3, 6, 7, 8, 9. Below is a list of country calling codes for various states and territories in Asia.Telephone numbers in Europe
Telephone numbers in Europe are managed by the national telecommunications authorities of each country. The country calling codes start primarily with 3 and 4, however, some countries that by the Copenhagen criteria are considered part of Europe have country codes from the Asia range, starting with 9.
The international access code (trunk prefix) has been standardized as 00, as recommended by the International Telecommunication Union (ITU).Telephone numbers in France
The French telephone numbering plan is not only used for metropolitan France but also for the French overseas departments and some overseas collectivities.
The plan uses a ten-digit closed numbering scheme, where the first two digits denote the area:
02 Northwest France
03 Northeast France
04 Southeast France
05 Southwest France
06 Mobile phone services
07 Mobile phone services
08 Special phone numbers: Freephone (numéro vert) and shared-cost services.
09 Non-geographic number (used by Voice over IP services)All geographic numbers are dialed in the ten-digit format, even for local calls. The international access code also changed from 19 to the International Telecommunication Union's recommended 00, bringing France into line with many other countries.
When calling France from abroad, the leading zero should be omitted: for example, to call a number in Southwest France, one would dial +33 5 xx xx xx xx.
French people usually state phone numbers as a sequence of five double-digit numbers, e.g., 0x xx xx xx xx (and not, for example, 0 xxx xxxxxx xxx or 0xxx-xx-xxxx or 0xx-xxx-xxxx).Telephone numbers in Indonesia
Telephone numbers in Indonesia have different systems for land lines and mobile phones: land lines use area codes, while mobile phones do not.
For land line area codes, the digit "0" is added in front when dialing domestic long distance from within Indonesia, but is always omitted when calling from abroad. Instead, callers would use the Indonesian country code +62, followed by the area code, without the "0". Domestic phone numbers in large cities have 8 digits, and in other areas 7 digits. Mobile phone numbers have a total of 10 or 11 digits for postpaid depending on the operator, whereas prepaid services get 11 to 12 digits determined by the operator.
Until October 1999, East Timor was included in the Indonesian telephone numbering plan, using the area codes 0390 (for Dili) and 0399 for (Baucau).
To make a phone call to Indonesia from abroad, the following formats are used:
For calls to landlines, callers dial +62, followed by the area code and subscriber's number, omitting the '0', hence a number in Jakarta would be dialled as +62 21 xxx xxxx.
For calls to mobile wireless phone (GSM) from abroad, callers dial +62, followed by the subscriber's number, omitting the '0', hence +62 95410537962Telephone numbers in Italy
Telephone numbers in Italy are defined by a telephone numbering plan that is organized by types of services. Landline numbers and mobile phone numbers are easily recognizable: the former start with 0 and the latter start with 3. Other initial digits denote other services, such as emergency and toll-free numbers.
The country code for calling Italy from abroad is 39. The international prefix is 00, as is standard in most European countries. Four different emergency numbers exist, including 112.Italy uses an open numbering plan in which the length of subscriber telephone numbers varies from six to eleven digits. The dialing procedures for callers mandate that the full telephone number is always dialed, including the area code, which is called prefix (prefisso in Italian).
When communicating phone numbers it is usual to group the digits, but there are no fixed rules for grouping. The same phone number is likely to be written or pronounced differently by different people. Several symbols can be used to group digits; spaces are common, but dots and hyphens are often seen as well.Telephone numbers in Macau
Telephone numbers in Macau are eight-digit numbers. Fixed land line numbers starts with 2, and Mobile (cellular) phone numbers starts with 6. Calls from Macau to mainland China, Hong Kong, Taiwan and Portugal are treated as international calls.
The telephone number for emergency services – Police, Fire Service and Ambulance – is 999 for all telephone lines. In addition to 999, two more emergency hotline numbers 110 (mainly for tourists from mainland China) and 112 (mainly for tourists from overseas) can be dialed, however calls made to 110 and 112 are redirected to the 999 call centre.Telephone numbers in Malaysia
Telephone numbers in Malaysia are regulated by the Malaysian Communications and Multimedia Commission (MCMC).
Landline telephone numbers consists of an area code of 1 to 2 digits (excluding the leading zero) followed by a 6 to 8-digit subscriber number. Mobile phone numbers consists of a mobile phone code of 2 digits followed by a 7 to 8-digit subscriber number. Mobile phone codes are originally assigned to specific mobile network operators, however with mobile number portability, a mobile phone number might no longer be associated with its original assigned operator.
Until 2017, calls to Singapore did not require international dialling; calls were made using the 02 domestic access code. However, following a directive from MCMC, it was discontinued in stages in May and June 2017. It was discontinued early on 16 May 2017 by Telekom Malaysia, and discontinued entirely by other Malaysian telecommunications companies on the 1st. of July 2017. The normal international prefix of 0065 has been made mandatory after that date. Similarly, calls to Brunei from East Malaysia can be made using the 080 domestic access code but calls from Peninsular Malaysia to Brunei require the international prefix 00673.Telephone numbers in Singapore
Telephone numbers in Singapore, also known as the National Numbering Plan, are regulated by the Info-communications Media Development Authority (IMDA). Due to the small geographical size of Singapore, there are no area or trunk codes; all numbers belong to one numbering area, and thus come in the same 8-digit format. Numbers are categorised based on the first digit, thus providing ten possible categories, of which six are currently in use and the remaining four reserved for future usage.Telephone numbers in South Africa
South Africa has switched to a closed numbering system. Within South Africa, from 16 January 2007 it became mandatory to dial the full 10 digit telephone number including the zero in the three-digit area code even for local calls (for example: 011 must be dialled from within Johannesburg). Area codes within the system are generally organized geographically. All telephone numbers are 9 digits long (but always prefixed by 0 for calls within South Africa), except for certain Telkom special services. When dialed from another country, the '0' is omitted and replaced with the appropriate international access code and the country code 27.
Numbers were allocated when South Africa had four provinces, meaning that ranges are now split across the current nine provinces.
South-West Africa (including Walvis Bay) was integrated into the South African numbering plan.Following its independence as Namibia, direct dialing from South Africa was discontinued and replaced by international dialling with the +264 country code. For example, for a call from South Africa to Windhoek, before and after 1992:
Before 1992: 061 xxx xxxx
After 1992: 09 26461 xxx xxxx
After Jan 2007: 00 26461 xxx xxxxCalls to Lesotho could be made using the access code 050 instead of the international code +266; for example, to call Maseru from South Africa, subscribers would dial 0501.Calls to Botswana, Swaziland and Zimbabwe could similarly be made using the regional codes 0192, 0194 and 0191, respectively, instead of the international codes +267, +268 and +263.Telephone numbers in South Korea
Telephone numbers in South Korea are organized and assigned using the following scheme.Telephone numbers in Spain
The Spanish telephone numbering plan is the allocation of telephone numbers in Spain. It is regulated by Comisión del Mercado de las Telecomunicaciones (CMT).Telephone numbers in Switzerland
Telephone numbers in Switzerland are defined and assigned according to the Swiss telephone numbering plan administered by the Swiss Federal Office of Communications. The plan has been changed several times and the most recent reorganization was implemented in March 2002.Telephone numbers in Turkey
Telephone numbers in Turkey went from six (2+4) to seven digits (3+4) local phone numbers c.1988, at which time Ankara went from 41 to 4. There used to be more than 5,000 local area codes of varying lengths (one to five digits) with correspondingly varying local number lengths (seven to three digits).
The new system is based on 83 three-digit area codes for provinces and seven digit local phone numbers. Istanbul is the exception and it gets two area codes ((212) for the European and (216) for the Asian side).
Calling a cell phone from outside Turkey is the same except the three digit numbers are replaced with the ones of the companies. Like  +  + [cell company id number] + [seven digit number]. The following are the company identification numbers for the major mobile telephone providers: Turkcell (530-539, 561), Vodafone (540-549) and Türk Telekom (500-509 and 550-559).
Local numbers in most areas were also changed in conjunction with the numbering plan that took effect 1 August 1993.
If a former area code is indicated, this is for the major centre in the new area code's district. The new area codes will also replace former area codes other than the primary one mentioned.Telephone numbers in the Americas
All countries in the Americas use codes that start with "5" except for: Canada, the United States and some Caribbean countries under the North American Numbering Plan use country calling code 1 and Greenland and Aruba with a country calling code starting with the number "2", which mostly is used by countries in Africa.Telephone numbers in the United Kingdom
Telephone numbers in the United Kingdom are administered by the UK government's Office of Communications (Ofcom). For this purpose Ofcom established a telephone numbering plan, known as the National Telephone Numbering Plan, which is the system for assigning telephone numbers to subscriber stations.
The numbers are of variable length. Local numbers are supported from land-lines, or numbers can be dialled with a '0'-lead prefix that denotes either a geographical region or another service. Cell phone numbers have their own prefixes which are not geographical and are completely portable between providers.