Beginning in 1947, the United States and Canada (and eventually several other countries and territories) formed a unified telephone numbering scheme called the North American Numbering Plan, or NANP. Under the plan, each telephone number consists of a three-digit area code (or Numbering Plan Area code, NPA for short) and a seven-digit local number. The original map had 86 area codes, although Alaska, Hawaii, and the Caribbean were not yet included. Just 50 years later, there were over 200 area codes, and in the 21st century, that number has gone well over 300!
The original plan distinguished between area codes and local numbers by careful assignment of number ranges. Neither area codes nor local numbers can begin with 0 or 1. The second digit of an area code was always 0 or 1, and the second digit of a local number was never 0 or 1. This distinction allowed the telephone network to determine by examining the first three digits of the dialed number, whether the number was in the local area or long distance.
Over the years, several area codes were split or realigned to ensure that each region had adequate numbering capacity for its needs. As more and more telephone lines came into use, through population and economic growth, the expansion of technologies such as DID PBXs (direct inward dialing private branch exchanges, which allow you to dial an individual’s extension without going through the company receptionist), and the introduction of new technologies such as telephone fax machines, modems, pagers, and cellular phones, an increasing number of area codes were filling to capacity and requiring relief in the form of area code splits. In the early 1970s, a plan was formulated to deal with this increasing demand: in the first stage, local numbers would be permitted to have the second digit be a 0 or a 1, first in areas of very high demand such as Los Angeles and New York City, and later in other metropolitan areas. The second stage was put into effect in 1995, allowing area codes to have any arbitrary number as the second digit. The combination of these two measures increased the total numbering capacity of the NANP by more than a factor of five.
The next step in the expansion of North American telephone numbers will take place some time in the late 21st century, when ten-digit telephone numbers no longer provide adequate capacity. All area codes with 9 as the middle digit are reserved for this future expansion, although there are proposals (including mine), that would allow for the immediate use of the N9X codes while still providing an orderly transition to longer-than-10-digit numbers.
The pages in this site contain detailed information about the history and near future of area codes. In addition, you will find detailed information about international telephone and Internet country codes.
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