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, 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, area code, prefix, and subscriber number.