Last updated
Notation for national and international telephone numbers, e-mail addresses and web addresses
Phone number setup.png
StatusIn force
Latest version(02/01)
February 2001
Organization ITU-T
Related standards E.163, E.164
Domain telephony
LicenseFreely available
Website https://www.itu.int/rec/T-REC-E.123

E.123 is an international standard by the standardization sector of the International Telecommunications Union (ITU-T), entitled Notation for national and international telephone numbers, e-mail addresses and Web addresses. [1] It provides guidelines for the presentation of telephone numbers, email addresses, and web addresses in print, on letterheads, and similar purposes.


As described by the ITU, in E.123: "+" is the "International Prefix Symbol" used in "Telephone number, E.112323 international notation".

Example formats

Telephone number, national notation (full number dialing)(0607) 123 4567
Telephone number, E.123 international notation+22 607 123 4567
Email addressexample@example.com
Web address / URL www.example.com

Telephone number

In the international telephone number notation, the leading plus (+) serves as an international prefix symbol, and is immediately followed by the country code. The user or the telephone system should replace the + symbol with international dialing prefix used in the caller's location.

Parentheses are used in national notation to indicate digits that are sometimes not dialed, such as area code in variable-length dialing numbering plans. Parentheses are not allowed in the international notation, according to the standard, as international callers use fixed number dialing.

For digit grouping, E.123 specifically recommends that:

No recommendation is made for grouping rules for digits in the local number, instead some examples of commonly used groupings are shown.

In national notation, the trunk prefix can be included with the area code if required by national writing conventions; trunk prefix is included in most European countries whenever they use fixed or variable dialing, but is omitted in USA and Canada where phone numbers only indicate optional area code.

A tilde (~) indicates an additional dial tone that the user should wait for.

A slash (/) with spaces on either side may be used to indicate alternative ending for numbers (i.e. "555 1234 / 4444" means 555 1234and555 4444).

The non-dialable PBX (private branch exchange) extension number should be separated by words "extension" or "ext." in the national language after the phone number.

When the PBX is capable of direct inward dialing, the extension number should be written directly after the phone number, without using any distinct symbols. If there is a need to indicate in-dialing capability of the telephone number, a number of dots (....) corresponding to the length of the extension number can be added at the end.

Microsoft telephone number format

Microsoft canonical address format for telephone numbers [2] [3] derives from E.123 international notation by allowing explicit indication of area code with parentheses.

The canonical format is used by the Telephony API (TAPI), a Windows programming interface for dial-up fax, modem, and telephone equipment. Depending on the user's current location, the Windows' Dial-Up Networking (DUN) component applies a set of dialing rules to transform the canonical phone number into a locally dialable calling sequence for the modem device. The dialing rules may include variable-length dialing for area code, trunk access and international access prefixes, central office/service access numbers, and calling cards tone numbers. [2] [3]

With this approach, phone numbers stored in the phone book remain unchanged when the user moves to a different geographical location or selects a different phone service provider. [4]

The calling sequence can contain dialable numbers such as digits 09 and DTMF tones ABCD*#, formatting characters ␣ . -, and control characters ! P T , W @ $ ? ;, which correspond to the Dial command of the Hayes AT command set.

Emergency contact information

A standardized language-independent way to identify a next-of-kin (or other emergency contact) in a mobile handset’s directory, in case of an emergency, has in May 2008 been adopted as a new clause in Recommendation E.123.

It proposes to store emergency contact numbers prefixed with Arabic numerals in the form “0nxxxx”; “n” is a digit from 1 through 9 and “xxxx” is any meaningful descriptive character string in any language or script (e.g. “Anna” or “Spouse”).

In the handset's directory this would be displayed as "01Anna" or "01Spouse" enabling easy identification by the emergency services. The handset’s directory entry (in the “contact number” field) would contain the actual number of the person to call in case of emergency. [5]

This scheme is a language-independent version of the "ICE" (In Case of Emergency) scheme that became popular in certain parts of the world from 2005 onwards. [6] [7]

See also

Related Research Articles

The Telephony Application Programming Interface (TAPI) is a Microsoft Windows API, which provides computer telephony integration and enables PCs running Microsoft Windows to use telephone services. Different versions of TAPI are available on different versions of Windows. TAPI allows applications to control telephony functions between a computer and telephone network for data, fax, and voice calls. It includes basic functions, such as dialing, answering, and hanging up a call. It also supports supplementary functions, such as hold, transfer, conference, and call park found in PBX, ISDN, and other telephone systems.

E.164 ITU-T Recommendation

E.164 is an international standard, titled The international public telecommunication numbering plan, that defines a numbering plan for the worldwide public switched telephone network (PSTN) and some other data networks.

The North American Numbering Plan (NANP) is a telephone numbering plan for World Zone 1, which comprises twenty-five distinct regions in twenty countries primarily in North America, including the Caribbean. Some North American countries, most notably Mexico, do not participate in the NANP.

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 the administrative regions of the public switched telephone network (PSTN) and in private telephone networks.

Telephone numbers in Australia Wikipedia list article

The Australian telephone numbering plan describes the allocation of phone numbers in Australia. It has changed many times, the most recent major reorganisation by the Australian Communications and Media Authority taking place between 1994 and 1998.

Area code 868

The area code 868 is assigned to Trinidad and Tobago, a member of the North American Numbering Plan (NANP). The telephone numbering plan for the country is known as the National Numbering Plan. It is part of a system used for assigning telephone numbers in Trinidad and Tobago, and functions as a part of the North American Numbering Plan (NANP). It is regulated by the Telecommunications Authority of Trinidad and Tobago, which holds responsibility for telecommunications in the country.

A dial plan establishes the permitted sequences of digits dialed on subscriber or station lines with subscriber premises equipment, such as telephones and private branch exchange (PBX) systems. Dialing plans in the public switch telephone network (PSTN) have traditionally been more commonly referred to as dialing procedures. The dialing plan of a private telephone system or a customer premise equipment, such as an analog telephone adapter (ATA) or an IP phone, is sometimes also called dial plan. The digit sequences (numbers) permissible in a dialing plan may be as short as a single digit, e.g. for reaching an operator, or as long as a complete international telephone number, including trunk prefixes and international prefixes.

Area code 246 is the telephone area code in the North American Numbering Plan (NANP) for Barbados. Telecommunication services in Barbados are regulated by the Government of Barbados's telecommunications unit. The number 246 spells BIM on an alpha-numeric telephone keypad, a nickname for the island.

A trunk prefix is a digit sequence to be dialed before a telephone number to initiate a telephone call for the purpose of selecting an appropriate telecommunications circuit by which the call is to be routed.

Widespread UK telephone code misconceptions, in particular brought on by the Big Number Change in 2000, have been reported by regulator Ofcom since publication of a report it commissioned in 2004.

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 New Zealand New Zealand numbering plan

The New Zealand telephone numbering plan describes the allocation of telephone numbers in New Zealand and the Pitcairn Islands.

Telephone numbers in the Philippines Wikipedia list article

Telephone numbers in the Philippines follow an open telephone numbering plan and an open dial plan. Both plans are regulated by the National Telecommunications Commission, an attached agency under the Department of Information and Communications Technology (DICT).

Telephone numbers in Italy Wikipedia list article

Telephone numbers in Italy are managed by the Autorità per le Garanzie nelle Comunicazioni (AGCOM), a national regulatory authority for the communication industry located in Rome.

All of Finland, including the Åland Islands, has the same country code, +358.

Telephone numbers in Thailand Wikipedia list article

Thailand's telephone numbering plan in Thailand is managed by the National Broadcasting and Telecommunications Commission (NBTC) in accordance with International Telecommunications Union's (ITU) recommendation E.164.

Telephone numbers in Canada follow the fixed-length Bell System format, consisting of the country code +1, followed by a three-digit area code, a three-digit central office code and a four-digit station code. This is represented as 1 NPA NXX XXXX, in which the country code is "1".

The national conventions for writing telephone numbers vary by country. While international standards exist in the form of the International Telecommunication Union sector ITU-T issued recommendation E.123, national telephone numbering plans define the format and length of telephone numbers assigned to telephones.

Telephone number Sequence of digits assigned to a telephone subscription

A telephone number is a sequence of digits assigned to a fixed-line telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices for data transmission via the public switched telephone network (PSTN) or other public and private networks.


  1. "E.123 : Notation for national and international telephone numbers, e-mail addresses and web addresses". www.itu.int. Archived from the original on 2019-11-11. Retrieved 2019-11-11.
  2. 1 2 MSDN: TAPI Applications - Device Control - Canonical Address
  3. 1 2 Microsoft Technet: Dialing Rules and Canonical Address Format.
  4. MSDN: TAPI Applications - Device Control - Storing Phone Numbers in Electronic Address Book.
  5. "ITU standard allows emergency rescue workers to identify a victim's next-of-kin". ITU-T Newslog. International Telecommunication Union. 20 May 2008. Archived from the original on 19 October 2016. Retrieved 24 May 2008.
  6. Bob's idea has global impact (Cambridge Evening News) Archived February 3, 2009, at the Wayback Machine
  7. Canada Phone Numbers