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Trunk prefix

Telecommunications technology

Wikipedia contributorsAdapted for Fathomly · View authors
3 min read
Source updated January 20, 2026

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.

01Methodology

Telecommunication networks evolved from small, locally designed and managed networks within a city, region, state, province, etc. and grew by geographic expansion and the desire to communicate across the boundaries of such networks. For this purpose special trunks became available by which calls are routed for interconnection of different networks. The telephone numbering plans were typically incompatible with those in other networks. Telephone companies enabled the routing via external trunks to other networks by requiring operators or subscribers to dial special prefix sequences prior to dialing the destination telephone number.

Before the implementation of direct distance dialing (DDD) in the United States, operators used routing codes to select specific trunks to the next intermediate destination, or, in Operator Toll Dialing, an area code to forward the call to a remote numbering plan area toll switch. In Direct Distance Dialing the newest local (Class 5) switching systems did not require special prefixes in addition to the area code, but older systems were retrofitted with equipment that enabled a toll trunk by dialing a special prefix sequence.

Today, making a domestic (national) telephone call usually requires the dialing of a single or two-digit national trunk prefix preceding any area codes and the destination subscriber number. In most countries, the trunk prefix is 0.

For international telephone calls the caller must dial an international trunk prefix, followed by the destination's country code. Many mobile telephone systems also permit dialing the character + in place of the International trunk prefix to automatically substitute the appropriate code for the origination country.

For displaying an international telephone number in directories, business cards, or stationery, a telephone number is represented by prefixing it with a plus sign and the country code, without any local trunk prefixes.

02Countries using national trunk prefixes

Countries that use 0 as national trunk prefix

Africa

South America

Asia

Europe

Oceania

Countries that use 8 as national trunk prefix

Countries that use other trunk prefixes

The number next to a country denotes its national trunk prefix.

03Countries that no longer use a national trunk prefix

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Sources and credits

This article is adapted from the Wikipedia article “Trunk prefix”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.

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Related topics

Subscriber trunk dialling

Subscriber trunk dialling, also known as subscriber toll dialing, is a telephone numbering plan feature and telecommunications technology in the United Kingdom and various Commonwealth countries for the dialling of trunk calls by telephone subscribers without the assistance of switchboard operators. Switching systems to enable automatic dialling of long distance calls by subscribers were introduced in the United Kingdom on 5 December 1958, using destination codes that were based on the letters in a town's name.