The telephone prefix for a city can be found on websites on the Internet where the area codes for each city are listed by city. Most sites also include an area code map that displays the telephone prefix by geographic location.
Telephone prefixes are often called area codes or NPA codes, with NPA an acronym for numbering plan areas. Free sites list the area code for a particular area as well as the timezone and city. The area code is present in the United States, U.S. territories, Canada and the Caribbean.
The North American Numbering Plan Administration, or NANPA, is the organization that determines the way area codes are assigned. The NANPA also assigns area codes to different phone companies so that they can then assign those area codes to their customers. For these countries the phone number follows the NPA-NXX-XXXX format. After the area code, the next three digits are the NXX code. This NXX code is also known as an exchange or simply a prefix.
There are many NPA code and NXX code combinations, but not all are used. Only 316 area codes are used out of the possible 1,000 area codes available. There are 1,601,380,000 possible combinations made up of NPA and NXX combinations. The population in the U.S. and Canada, according to World Bank statistics, reveals that there are enough combinations for every person to have four telephone numbers.