Telephone prefix

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A telephone prefix is the first set of digits after the country, and area codes of a telephone number. In the North American Numbering Plan countries (country code 1), it is the first three digits of a seven-digit local phone number, the second three digits of the 3-3-4 scheme. In other countries, both the prefix and the number may have different lengths. It shows which exchange the remaining numbers refer to. A full telephone number is usually made up of a country code (required for international calls only), area code (required for calls between telephone areas), prefix, and subscriber number.

Some places restrict certain prefixes to fax numbers or cell phones only; in other places such dedicated prefixes are not used.

As telephone technology advanced, the precise significance of the prefix became blurred in many places; for instance, 485 in London, UK, was once the GULliver exchange, but now 44-20-7485-xxxx is just considered one of many number blocks served by the CLKEN Kentish Town exchange.^[1]