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Glossary -->

The following words relate to telephone numbering, and may appear in WTNG:

area code

An area code is used within many nations to route calls to a particular city, region or special service. Depending on the nation or region, it may also be referred to as a numbering plan area, subscriber trunk dialling code, national destination code or routing code.

country code

A country code is used to reach the particular telephone system for each nation or special service.

World Zone

The World Zone is the first digit of a country code. This generally corresponds to a global region, but some country codes are an exception (e.g. +299 Greenland is not in Africa, but there was not enough room in Europe's two World Zones at the time Greenland's country code was originally assigned). Special international services such as freephone or satellite telephone have country code assignments under World Zones 8 and 9.

closed numbering plan

A closed numbering plan refers to a telephone numbering scheme that has a fixed number of digits, not counting special service codes. The North American Numbering Plan +1 is an example, because there are always ten digits associated with each national number - 3 digits of area code followed by 7 digits of subscriber number. Australia +61 has become another example of a closed numbering plan.

trunk prefix

A trunk prefix refers to the initial digit(s) to be dialled in a domestic call, prior to the area code (if necessary) and the subscriber number. 0 is the trunk prefix in most nations. In the North American Numbering Plan +1 it is 1; it is merely co-incidental that the country code and trunk prefix are both 1. For calls to another country code, the trunk prefix is generally omitted. For example, a call to London, UK within the UK would be dialled as 020 #### #### but from outside the UK, the initial 0 (trunk prefix) is omitted: +44 20 #### ####. Some nations do not use a trunk prefix, which means only the subscriber number is dialled in those cases.

international prefix

An international prefix is the code dialled prior to an international number (country code, area code if any, then subscriber number). In most nations, this will be 00. In some nations in Asia, this is 001 (in some cases, alternate codes are available to select the particular international carrier). In North America, this is 011 (or 01 for special call processing - collect, person-to-person, calling card, etc.).

closed dialling plan

A closed dialling plan refers to a national requirement to use all digits of a national number (often including a trunk prefix) to place a call, whether local or long distance. The current systems in France (as of October 1996) and Belgium (as of January 2000) are examples of closed dialling plans.

geographic area code

A geographic area code refers to an area code that has a defined geographic boundary. Geographic area codes are for conventional fixed-line (or land line) services terminating at fixed points. Non-geographic area codes would include wireless (cellular and pager whose subscribers could be located at variable points), or toll-free services (usually assignable on a nation-wide basis, without being bound to specific regions), or premium and personal number services (again, assignable anywhere within a nation).

local number, subscriber number

The local number or subscriber number represents the specific telephone number to be dialed, but does not include the country code, area code (if applicable), international prefix or trunk prefix.

national number

The term national number in this document refers to the combination of area code (if any) plus local number.

permissive dialling period

A permissive dialling period is a time during which an old and new numbering format may be used to place calls to a subscriber. This is used to provide a transition phase, to allow telephone users time to adjust to a new numbering scheme.

mandatory dialling

After a permissive dialling period, the old numbering format becomes invalid and the new numbering format is said to be mandatory.

splash cut

A splash cut means a numbering change that is made without any interim permissive dialling period. The old numbering is suddenly replaced by a new numbering format, on a date and time scheduled by the telephone regulator and/or carrier(s).


An exhaust occurs when all available numbers in a numbering space have been assigned for some purpose - e.g. no more subscriber numbers can be assigned for an area code, because all assignable numbers are in use or otherwise unavailable for use. Normally, relief measures would be taken to add numbering capacity well before an exhaust occurs, usually through the assignment of additional area codes or extra digits.


An overlay refers to the assignment of a new numbering range in the same territory as an existing numbering range. For example, a new area code would be added within an existing area code's boundaries. Two subscriber lines in the same premises could then be assigned different area codes.


sterilisation refers to a period in which a decommissioned numbering range is left unused. For example, an area code may be changed to allow its range to be used for future area codes. However, it may not be desirable to re-assign the old code immediately, as callers may still attempt to use the old code for some time.

append, prepend

When a telephone number is changed by adding a digit before the existing number, the digit is said to be prepended. On the other hand, a digit added after the end of an existing telephone number is appended.


Note that some numbering terms, such as prefix, often mean different things in different places e.g. a prefix could be the digits dialled before a long distance call, or it could refer to an initial part of a subscriber number that identifies a location or type of service.

WTNG attempts to consistently use the terms trunk prefix and international prefix as defined above.

plus sign (+) notation for country codes

Where a plus sign (+) is used, this indicates a country code (e.g. +33 for France), or it may indicate the initial portion or complete number as it is dialed in international format (e.g. +52 5 represents Mexico City - +52 Mexico country code, then area code 5).

carrier, operator

A company providing a telephone service (whether wireline, wireless, etc) is a carrier or operator.


WTNG does not have the final word on telecom terminology; the job of describing the rapidly-changing field of telecom numbering is a continuing challenge.

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