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The North American Numbering Plan Administration (NANPA) is governed by the North American Numbering Plan Administration. The NANPA organizes the allocation of area codes and telephone prefixes to various phone companies. The basic format of a phone number is NPA-NXX-XXXX or (NPA) NXX-XXX.

NPA codes are often called area codes. Some area codes are for private use. For example, an area code of 800 (commonly referred to as an 800-number) is reserved for a free call, where the calling party is charged instead of the called party. Also, not all area codes are currently in use. Only 316 of the possible 1000 area codes are used.

The fixed line number or the next three names of the cell phone are called NXX. NXX is also known as prefix or exchange. Various telephone operators divide the blocks of telephone numbers by holding an NXX in an area code. Like area codes, not all prefixes are used at the moment. Currently only 160.138 prefixes are used.

Finally, the last 4 digits of the phone number are known as the subscriber or local number. Based on the total number of active NPA and NXX segregated and each having 10,000 possible subscriber numbers, the total number available is 1.601.380.000. According to the United States Population and World Bank, there are 4 telephone numbers for each person according to the total population of the United States and Canada. Please note that these phone numbers are no longer used only for standard home phones. Many phone numbers are now used for fax machines, mobile phones or cordless phones or internet connections; For this reason one person may actually need more than one phone line.