Phone number

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Components of a telephone number

A call number or telephone number (often abbreviated to Tel. For address details , and for some time also to Fon or Phone ) is a sequence of digits for dialing a destination during a telephone conversation . In the narrower sense, subscriber number or direct dialing number refers to the number that occurs once within a local network . Fax numbers are numbers for dialing fax machines , dial-in numbers are numbers for dialing telephone modems over the telephone network. Certain instant messaging services such as B. SMS or WhatsApp also use phone numbers to address a recipient.

Word choice numbers (also called vanity numbers) contain letters instead of digits. During the actual dialing process, the letters are automatically translated into digits by entering them on a numeric keypad. Word choice numbers are not special numbers, just a memory aid .

Number assignment

Telephone numbers in the public telephone network are mainly assigned by telephone companies. These are linked to national numbering plans that are usually administered by national regulatory authorities. For example, the Federal Network Agency (BNetzA) manages the German number range . The broadcasting and telecommunications regulatory GmbH (RTR) managed Austrian numbers . The Federal Office of Communications (OFCOM) administers Swiss numbers .

In North America, several states have come together to form a common North American numbering plan . A European telephone numbering room has been set up in Europe .

The International Telecommunication Union coordinates international area codes and publishes the international numbering plan E.164 . The European Commission harmonizes telecommunications standards within the EU .


Area code for the phone number

In order to be able to dial a number with a telephone , additional digits often have to be preselected (or left out). The term telephone area code is used inconsistently. On the one hand, it includes traffic elimination digits (including outside line access ), geographical areas (such as local area codes ) and service codes (such as network selection in mobile communications and special numbers ) and, on the other hand, the international telephone prefixes (also known as country or country codes ).

The rules for converting a number into a dialable sequence of digits depend on the telecommunications provider of the caller. In order to reach a landline connection in Munich (“089 1234567”), a call-by-call user in Munich must dial different digits (“0101X 1234567”) than a mobile phone subscriber in the USA (“011 49 89 1234567” or "+49 89 1234567"). Extension lines also often have their own rules. A large part of these voting rules are laid down in the international and national numbering plans.

Code entries

The USSD codes must be distinguished from the actual telephone prefixes . Some are dialed before a telephone number, but are commands to the telephone network. To distinguish it from the telephone number, the USSD numbers are framed by asterisks ( *) and / or hash characters ( #), e.g. B. #31#/ *31#for (not) transmitting the phone number. For some functions (e.g. setting up a forwarding to the mailbox) the "Infix" (cf. differences between area code and block identification limit ) is important.

Landline numbers

For historical and technical reasons, number assignment for the fixed network was tied to a specific location until the end of the 1980s. At the local level, subscriber or extension numbers could only be assigned connection-related, which is why you usually looked at the locality or district (except for external connections ). The respective area code, and later country code, completed the geographic relationship of these numbers, which is why they were also called geographic numbers .

In the fixed network, phone numbers are divided into

  • Country code (LKz)
  • Area code (ONKz), and the
  • Subscriber number (RufNr), if the subscriber is directly connected to a local exchange,


  • Country code (LKz)
  • Area code (ONKz), and
  • Direct dialing number, consisting of the base number and extension number , if the subscriber is connected to a telephone system .

In order to dial a national landline connection, a traffic code must be added to the dialed number when dialing into another local network .

In the case of a call within a local area network, the area code can be omitted. This convenience has been retained with IP connections, although nomadic use is also possible in other local networks. In this case, however, the local network is not the one in which the subscriber is actually located, but rather that to which he is connected according to the number plan. From a technical point of view, the subscriber's local network number is defined as the standard and automatically added by the provider's server if the area code is missing.

An outside line must be preselected if the calling subscriber is in a non-public or private network.

Service provider or network operator codes (carrier code) can be inserted, for example “city carriers” or “national carriers”. This is not possible with every provider.

Thanks to the digitization of switching technology, it has also been possible to transfer phone numbers in the fixed network since the 1990s . "Fixed line numbers" can now be assigned to any connection. Number portability is mandatory for IP telephony , as there is no dependency between the physical connection line and the number. The allocation of "landline numbers" is regulated differently in different countries today.

Traffic to numbers with local area code can be forwarded to another local area network, but the costs incurred will be charged to the called party from the dialed local area network number to the forwarding destination. The local reference can be technically bypassed when using internet telephony (“nomadic use”), but in Germany the Federal Network Agency still stipulates the binding of local area codes for connections within a local area network. In order not to be tied to a fixed geographical allocation with such connections, the Federal Network Agency has introduced a national subscriber number with the area code 032 as an alternative . In other countries, such as Switzerland and Denmark, subscriber numbers including the area code can also be ported without receiving a new number in the new local area network, so that in practice the distinction between regional and national numbers is no longer necessary.

Cell phone numbers

Numbers for cell phones are assigned according to different rules. In large territorial countries, such as the USA, mobile phone connections have geographical telephone numbers in order to be able to better bill the increased costs for national long-distance switching (see also NANP ). This makes it easier for the calling subscriber, on the one hand, to determine his costs before a call, on the other hand, he only pays for the distance to the home cell of the called party, the further distance is borne by the called party, the so-called roaming fee .

In Germany, when mobile communications were introduced, special area codes were created. With the prefix 015x, 016x, 017x, a mobile phone number can be recognized immediately. The area codes are assigned to individual mobile phone companies (see also telephone code (Germany) ). Until the introduction of number portability in 2002, the caller could also deduce the mobile phone company from the area code.

In Austria, the area codes of the cellular networks begin with the sequence 06xx. However, since the area codes in the federal state of Salzburg and partly in nearby Upper Austria begin with 06xx, it is not easy to infer from the area code whether it is a mobile or landline number (see also telephone area code (Austria) ).

Special numbers

For some services, abbreviated numbers or special area codes (number ranges) are provided at national level . The call tariffs for these special numbers differ greatly from calls to regular landline or mobile phone connections. Some services are free for the caller, such as emergency numbers or 0800 numbers. Other services sometimes charge very high tariffs.

Examples of abbreviated numbers:

Examples of special area codes:

In addition, mobile network providers assign special short code numbers for SMS .


There are numerous standards for the spelling of telephone numbers in printed matter and business letters . Most influential internationally are Recommendation E.123 of the International Telecommunication Union and the Microsoft canonical address format . In Germany, DIN 5008 is decisive. There are no separate standards for Austria; RTR refers to E.123 and DIN 5008.


National phone numbers in Germany are shown as follows:

Notation Remarks
030 12345-67 DIN 5008 : Functional structure with spaces. Extension with a hyphen
0900 5 123456 DIN 5008 : Separate content indicators (here: "5") for value-added services with spaces.
(030) 12345 67 E.123 : Area code in brackets if it is not always selected. If necessary, structure with spaces.
(030) 12345 67/89 E.123 : Means that either 67 or 89 can be chosen at the end.
0 30/12 34 56 Usual, non-standardized variant: Division into groups of two with spaces, the area code separated by a slash

The following examples of international numbers contain the country code 49, the area code 30, the subscriber number 12345 and the extension 67:

Notation Remarks
+49 30 12345-67 DIN 5008 : Function-related separation by spaces, direct dialing separated by a hyphen .
tel: + 49-30-1234567 Uniform Resource Identifier according to RFC 3966 ; like E.123 , but with a hyphen instead of a space
+ 49.3012345x67 Extensible Provisioning Protocol (EPP) according to RFC 5733 ; derived from E.164.
+49 (30) 12345 - 67 Microsoft's canonical address format (TAPI): Area code in brackets, no specifications for subdividing subscriber number and extension, but the extension is separated with a hyphen .
+49 (0) 30 12345-67 Notation that is widespread in Germany and Austria, but does not conform to the standards: traffic elimination number 0 is inserted in brackets. With the automatic number recognition z. B. mobile devices it can lead to errors, because the number is invalid because of the inserted zero and dialing is therefore not possible.


The following notation is recommended in Austria:

Notation Remarks
+43 1 58058-0 International, extension with hyphen
01 58058-0 National, extension with hyphen


The following spellings for telephone numbers are common in Switzerland:

Notation Remarks
026 324 11 13 Domestic representation - the slash previously used between the area code and the number has been obsolete since 2002, as this must always be dialed.
+41 26 324 11 13 International representation - as in Germany or Austria, the bracketed "(0)" of the area code is sometimes also written.

Length of phone numbers

Specification E.164 limits the length of telephone numbers in international traffic to a maximum of 15 digits, including the country code , excluding traffic exclusion digits . The Berlin number +49 30 1234567 therefore has eleven digits.

Since mid-2011, local network numbers (with ONKz, but without the traffic elimination number) have generally been assigned with eleven digits in Germany, with the exception of individual numbers in the local networks of Berlin, Hamburg, Frankfurt and Munich with ten digits. However, more than 15 digits can be used in national traffic, especially for special numbers.

The 3GPP standards for cellular networks provide a BCD-coded area of ​​10 bytes for the call number ("Dialing Number / SCC String") . The traffic elimination number or a leading "+" is not counted, but encoded in a separate byte (TON / NPI - type of number / numbering plan identification). If the MSISDN is longer than 20 digits, the additional digits are entered in extension blocks (EF EXT1 ), each providing a BCD-coded area of ​​11 bytes. The subscriber number of a maximum of 20 digits can be expanded by additional function digits in order to implement additional services . The ISDN subaddress , which is transparently transported through the telephone network, is technically limited to 20 BCD-coded bytes and is usually limited to 32 digits.


Since in the 1970s only 12 digits could be processed, especially in telephone systems of the Eastern Bloc, the total numbers were shortened for large companies using different methods at least in the following two cases:

  • Linz , formerly accessible under the area code 7222, received a 3-digit area code with 732 on October 1st, 1977 like most of the provincial capitals. So that the steel company VOEST can be reached with a 3-digit subscriber number and 5-digit extensions with 12 digits, the 2-digit code 70 for Linz was also introduced in the 1960s or 1970s - without public announcement and only accessible from abroad before 1997. which only worked until May 12, 2014 - (00) 43 70 585-12345 has 12 digits.
  • The large research institute GSI in Darmstadt , founded in 1969, got the telephone connection in the neighboring town of Messel , as a two-digit subscriber number was only available in this local network, with a 4-digit area code and 4-digit extensions in the GSI, as in Darmstadt. (00) 49 6159 71-1234 has 12 digits.


Telephone numbers are also personal data in terms of data protection . Dealing with your own numbers and those of others has an impact on the privacy of those affected.

In the digitalized public telephone network, the caller's number is usually transmitted to the person called. About call processing features the display of phone numbers as CLIP, CLIR, CLIRO, COLP can be suppressed or force.

Telecommunication providers save the phone number as part of the connection data that is necessary for processing and billing a telephone call. In Germany, they have no longer been legally obliged to retain data since 2010 .

By an entry of the telephone number in a public phone directories ( phone book , directory assistance assigning person and telephone number in a public database is stored). An inverse search can be used to identify the owner of a telephone number.

As protection against unwanted calls , secret numbers , i.e. numbers that cannot be queried via public telephone directories, are suitable . In some countries, so-called "disposable numbers" are offered, from which calls are forwarded to the connection to be protected for a limited time. These numbers are used primarily to avoid spam . Most of the time, the numbers expire by themselves after a certain period of time, in some other cases they are manually deregistered or simply no longer used.

In Germany, these special numbers, which were extended by several digits (regular 0180 number, extended by additional number digits contrary to the standard) were only temporarily tolerated in the early days of Internet telephony . The Federal Network Agency justifies this prohibition by stating that the forwarding of an extended number to end customers does not allow third parties to identify this subscriber. A corresponding documentation obligation of the operators of such numbers, for example in the case of an official prosecution, has not been implemented by the legislator.

History of number allocation

On April 1, 1881, Heinrich von Stephan opened the world's first telephone exchange, initially with eight subscribers. It was the first switching use of the telephone invented by Johann Philipp Reis and Alexander Graham Bell . In the same year, the first German telephone directory , ridiculed by the Berlin population as the “Book of Fools”, was published in Berlin with one, two and three-digit decadal numbers and 185 entries. The phone numbers were used to identify the terminal connections, which were again decadically arranged on the flap cabinets of the time .

Until 1905, all exchanges in the German-speaking area were hand-switched, connections were connected by giving the "phone number". Remote switching requests were passed on by additionally naming the cities. Decadal telephone numbers were not only clearly assigned to connection lines, historically they were actually “connection numbers” of the respective local area network. This should remain so for the next 100 years, and the introduction of the self-dialing remote service and the EMD voter changed little in this assignment. You could "take" your phone number (actually connection) with you when moving house, but only as long as your new place of residence was in the catchment area of ​​the same final exchange (10,000 area). The connection could then be "transferred" to the main distributor without canceling the assignment of call number to connection (corresponds roughly to a restricted number porting).

The decadal numbering was initially limited to the local level, but from 1923 onwards with the establishment of the first automated telephone exchange in Germany it was also used for direct dialing of other cities, in 1955 for the first time also for an automated international connection from Germany to Switzerland.

With the digitization of the telephone network at the end of the 1970s, and above all with the introduction of ISDN in the German-speaking countries at the end of the 1980s, a fundamental paradigm shift took place in the allocation of numbers: the complete separation of connection and number. This last step of end-to-end digitization in the fixed network opened up new routing options for the provider, regardless of whether the customer uses ISDN or an analog connection. In Germany, whose analog fixed network was not intended for routing between competing telephone networks, it was only because of this that competition between private telephone companies became possible, taking account of number porting. The connection no longer determined the call number, but a call number could be assigned to a connection at will. Since this separation, call numbers have only been used for addressing when dialing a target subscriber. Technically, its general function today is that of an abstract address. The direct consequences of this paradigm shift included:

  • multiple connections with one phone number, such as the hunt group feature for ISDN,
  • multiple numbers for one connection ( multiple subscriber numbers (MSN) in ISDN),
  • Landline numbers without connection, e.g. for system connection without connecting line or announcements,
  • Special numbers of the "intelligent network"
  • Complete porting options beyond the boundaries of main distributors or provider networks or between different network topologies (when porting between landline and VoIP)

With the advent of IP telephony in the mid-1990s, the only decadic classification of phone numbers also changed. The URI address used there made it possible for the first time to use alphabetic character strings for addressing, but only within a VoIP network.


International area codes, country codes and numbering plans:

National area codes, area codes and numbering plans:

See also

Web links

Wiktionary: phone number  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. a b Number management ( Memento of the original from April 11, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. the Federal Network Agency. (accessed May 30, 2010). @1@ 2Template: Webachiv / IABot /
  2. a b c National telephone numbers of the RTR. (accessed on March 21, 2008).
  3. a b Numbering & Telephony ( Memento of the original from April 3, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. of OFCOM. (accessed on March 21, 2008). @1@ 2Template: Webachiv / IABot /
  4. Telecoms in the European Union (accessed March 22, 2008).
  5. ^ Joerg Kilian: Communication standard for telephone numbers . ( Memento from January 25, 2009 in the Internet Archive ) May 2001. (accessed March 23, 2008).
  6. ^ Microsoft: Canonical address format for telephone numbers ( Memento of April 24, 2009 in the Internet Archive ). Status 2005. (accessed on April 24, 2009)
  7. FAQ: Is there a standardized way of writing phone numbers? Rundfunk und Telekom Regulierungs-GmbH (accessed on March 21, 2008).
  8. E.123: Notation for national and international telephone numbers, e-mail addresses and web addresses. ITU-T, February 2001, accessed February 4, 2019 (7.4).
  9. windows-sdk-content: Address - Windows applications. Retrieved February 4, 2019 (American English).
  10. Canonical Format - How to format phone numbers correctly in Outlook - Instructions. November 25, 2010, accessed on February 4, 2019 (German).
  11. Is there a standardized way of writing phone numbers? Rundfunk und Telekom Regulierungs-GmbH last accessed on December 4, 2017.
  12. spelling instructions . (PDF) Instructions from the Federal Chancellery on the writing and formulation in the German-language official federal texts. Swiss Federal Chancellery, 2008, p. 81 , accessed on May 18, 2013 .
  13. ^ Numbering concept 2011. ( Memento of February 24, 2013 in the Internet Archive ) Federal Network Agency; Retrieved January 11, 2012.
  14. Universal Mobile Telecommunications System (UMTS); LTE; Characteristics of the Universal Subscriber Identity Module (USIM) application (3GPP TS 31.102 version 9.18.1 Release 9) . ETSI. April 2017.
  15. RFC 4715: The Integrated Services Digital Network (ISDN): Subaddress Encoding Type for tel URI . IETF. November 2006.
  16. 0180 numbers with VoIP providers in danger., December 10, 2008.
  17. ^ "The first Berlin telephone directory 1881" ( Memento from August 7, 2013 in the Internet Archive ), editor: Gerhild Komander, reprint of the original from 1881.