Trunk prefix

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.

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, such as Australia, Germany and the United Kingdom, the trunk prefix is 0. In the North American Numbering Plan (NANP) states, such as the U.S. and Canada, it is 1. For international telephone calls, the national trunk prefix is not dialed; instead, an international trunk prefix is typically required. Many countries use the sequence 00, but in the NANP it is 011.

Assume that a call is to be made to a customer in the Australian Area/State of Queensland with the local number of 3333 3333 and the area code 7.

A caller from outside Australia must dial the international call prefix of the originating country, plus the country calling code (61 in the case of Australia), plus the area code (7 in this case), and then the local subscriber number. Therefore a caller in the U.K. must dial 00 61 7 3333 3333, while a caller in the U.S.A. must dial 011 61 7 3333 3333.

Calling inter-area (within Australia) (e.g. from Western Australia—area code 8), a caller need not dial an international trunk prefix or a country code. However, the caller must at least dial the Australian trunk prefix (0) followed by the area code (7) and then the local subscriber number: 07 3333 3333. Calling from within the Queensland (7) area, a caller need only dial the telephone number: 3333 3333.

However, because the world's telephone systems are "intelligent" enough to "know" from where the call has been originated, to where the call is directed and as to how it is to be charged, if the full international number is used, then this full international number may be dialed from any telephone anywhere. This is particularly important for users of mobile phones. Such users are strongly advised to store all numbers in their phones in the form of "+ (Country Code) (Area Code) (Local Number)", no matter where they live. Storing numbers in this manner will ensure that they can connect to any such stored number from any area or country in the world without any further consideration when they travel to any destination in the world.

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