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ITU-T Recommendation E.164
The international public telecommunication numbering plan
Phone number setup.png
StatusIn force
Year started1984
Latest version(06/20)
June 2020
Organization ITU-T
CommitteeStudy Group 2
Related standards E.123, E.163
Domain telephony
LicenseFreely available
Website https://www.itu.int/rec/T-REC-E.164/

E.164 is an international standard (ITU-T Recommendation), 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.


E.164 defines a general format for international telephone numbers. Plan-conforming numbers are limited to a maximum of 15 digits, excluding the international call prefix. [1] The presentation of a number at the B-party device is usually prefixed with the plus sign (+), indicating that the number includes the country calling code. This is done by the B-party subscribers network by usually looking at the NOA (Nature Of Address) field of the signaling messages. When dialing, the number must typically be prefixed with the appropriate international call prefix (in place of the plus sign), which is a trunk code to reach an international circuit from within the country of call origination. [2]

As described in by the ITU, the E.164 general format must contain only digits split as follows:

Alternative formats (with area codes and country specific numbers) are available.

The title of the original version and first revision of the E.164 standard was Numbering Plan for the ISDN Era+966502001668

Numbering formats

The E.164 recommendation provides the telephone number structure and functionality for three categories of telephone numbers used in international public telecommunication:

For each of the categories, it details the components of the numbering structure and the digit analysis required for successful routing of calls. Annex A provides additional information on the structure and function of E.164 numbers. Annex B provides information on network identification, service parameters, calling/connected line identity, dialing procedures, and addressing for Geographic-based ISDN calls. Specific E.164-based applications which differ in usage are defined in separate recommendations.

The number categories are all based on a fifteen-digit numbering space. Before 1997, only twelve digits were allowed. The definition does not include any international call prefixes, necessary for a call to reach international circuits from inside the country of call origination.

Geographic areas

National Destination CodeNational (significant)
cc = 1 to 4 digitsmaximum = 15 − cc = 11 to 14 digits
International public telecommunication number for geographic areas (maximum 15 digits)

Global services

Country CodeGlobal Subscriber Number
cc = 3 digitsmaximum 12 digits
International public telecommunication number for global services (maximum 15 digits)

[1] Figure 2


Country CodeIdentification CodeSubscriber Number
cc = 1 to 3 digitsx = 1 to 4 digitsmaximum = 15 − (cc + x) = 8 to 13 digits
International public telecommunication number for networks (maximum 15 digits)

Groups of countries

Group Identification Code
cc = 1 to 3 digitsgic = 1 digitmaximum = 15 − (cc + gic) = 11 digits
International public telecommunication number for groups of countries (maximum 15 digits)



E.163 was the former ITU-T recommendation for describing telephone numbers for the public switched telephone network (PSTN). In the United States, this was formerly referred to as a directory number. E.163 was withdrawn, and some recommendations were incorporated into revision 1 of E.164 in 1997. [3]


This recommendation describes the procedures and criteria for the reservation, assignment, and reclamation of E.164 country codes and associated identification code (IC) assignments. [4] The criteria and procedures are provided as a basis for the effective and efficient utilization of the available E.164 numbering resources.


This recommendation contains the criteria and procedures for an applicant to be temporarily assigned a three-digit identification code within the shared E.164 country code +991 for the purpose of conducting an international non-commercial trial. [5]


This recommendation describes the principles, criteria, and procedures for the assignment and reclamation of resources within a shared E.164 country code for groups of countries. [6] These shared country codes will coexist with all other E.164-based country codes assigned by the ITU. The resource of the shared country code consists of a country code and a group identification code (CC + GIC) and provides the capability for a group of countries to provide telecommunication services within the group. The Secretariat of the ITU Standardization Sector (ITU-T), the Telecommunication Standardization Bureau (TSB) is responsible for the assignment of the CC + GIC.

DNS mapping of E.164 numbers

Some national telephone administrations and telephone companies have implemented an Internet-based database for their numbering spaces. E.164 numbers may be used in the Domain Name System (DNS) of the Internet in which the second-level domain e164.arpa has been reserved for telephone number mapping (ENUM). In the system, any phone number may be mapped into a domain name using a reverse sequence of subdomains for each digit. For example, the telephone number +19995550123 translates to the domain name

When a number is mapped, a DNS query may be used to locate the service facilities on the Internet that accept and process telephone calls to the owner of record of the number, using, for example, the Session Initiation Protocol (SIP), a call-signaling VoIP protocol whose SIP addresses are similar in format (user@domain...) to e-mail addresses.

This allows a direct, end-to-end Internet connection without passing to the public switched telephone network (and back) and without incurring PSTN tolls.

As this is effectively a free call, there is little incentive for carriers to promote e164 DNS service. The e164.arpa domain is in production status as of 2013 only in a few European nations (Austria, Czech Republic, Finland, Germany, Ireland, Lithuania, Poland, Romania, Netherlands, United Kingdom). [7] Australia conducted a trial in 2007, but then abandoned further support of .1.6.e164.arpa. Many nations have no .e164.arpa implementation active. [8]

See also

Related Research Articles

Country code

Country codes are short alphabetic or numeric geographical codes (geocodes) developed to represent countries and dependent areas, for use in data processing and communications. Several different systems have been developed to do this. The term country code frequently refers to ISO 3166-1 alpha-2 or international dialing codes, the E.164 country calling codes.

Telephone number mapping is a system of unifying the international telephone number system of the public switched telephone network with the Internet addressing and identification name spaces. Internationally, telephone numbers are systematically organized by the E.164 standard, while the Internet uses the Domain Name System (DNS) for linking domain names to IP addresses and other resource information. Telephone number mapping systems provide facilities to determine applicable Internet communications servers responsible for servicing a given telephone number using DNS queries.

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.

E.123 ITU-T Recommendation

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. It provides guidelines for the presentation of telephone numbers, email addresses, and web addresses in print, on letterheads, and similar purposes.

MSISDN is a number uniquely identifying a subscription in a Global System for Mobile communications or a Universal Mobile Telecommunications System mobile network. It is the mapping of the telephone number to the subscriber identity module in a mobile or cellular phone. This abbreviation has several interpretations, the most common one being "Mobile Station International Subscriber Directory Number".

Universal personal telecommunications (UPT) is a special segment of the international telephone number space which has been set aside for universal personal telephone numbers. This service has been allocated country code +87810 and is completed by a 10-digit subscriber number which provides 10 billion unique numbers. The International Telecommunication Union (ITU) introduced this concept in 2001, referring to it as "global number portability". However, number portability normally refers to the service of keeping an existing phone number after moving service to another provider. The delegation of UPT was requested by VisionNG Chairman Herwart Wermescher and was confirmed by Counsellor, SG2 of ITU-TSB Richard Hill on May 21, 2002.

Telephone numbers in Azerbaijan Wikipedia list article

Telephone numbers in Azerbaijan follow the ITU Telecommunication Standardization Sector E.164 recommended format its telephone numbering plan.

Telephone numbers in Europe Wikipedia list article

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.

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 Sweden Wikipedia list article

In Sweden, the area codes are, including the leading 0, two, three or four digits long, with larger towns and cities having shorter area codes permitting a larger number of telephone numbers in the eight to ten digits used. Before the 1990s, ten-digit numbers were very rare, but they have become increasingly common because of the deregulation of telecommunications, the new 112 emergency number, and the creation of a single area code for the Greater Stockholm area. No subscriber number is shorter than five digits. The longest subscriber numbers have eight digits.

Telephone numbers in Taiwan

Telephone numbers in Taiwan use a system of area codes, beginning 02 to 08. The leading digit(s) following the area code denote the network operator. Mobile numbers begin 09. The international code for calls into Taiwan is 886.

Telephone numbers in Madagascar are seven digits long, the first two digits being an area code.

Telephone number Sequence of digits assigned to a telephone subscription

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Telephone numbers in San Marino are 6 to 10 digits long. Numbers starting with either 0, 8 or 9 are assigned to landlines, 6 is used for mobile services, 5 for IP telephony services and 7 for premium numbers. There's no trunk code: all the digits are always dialed.

Telephone numbers in Panama Wikipedia list article

All telephone numbers in Panama are seven or eight digits long and there are no area codes. All numbers beginning with 6 and with 8 digits are mobile numbers. All landline numbers have 7 digits. The first digit of landline numbers may be used to vaguely identify the location of the caller. Mobile phones were also assigned 7 digit numbers until 2005, when they were moved to their own number space with 8 digits. Mobile numbers are recycled if the user is marked as inactive by the mobile service provider, and landline numbers are also recycled if a user cancels their landline phone service.

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