2.2.3: Telephone Area Codes

The third way in which spare capacity can be used is by reserving it for future expansion. When AT&T started using telephone Area Codes for the United States and Canada in 1947 (they were made available for public use in 1951), the codes contained three digits, with three restrictions.

• The first digit could not be 0 or 1, to avoid conflicts with 0 connecting to the operator, and 1 being an unintended effect of a faulty sticky rotary dial or a temporary circuit break of unknown cause (or today a signal that the person dialing acknowledges that the call may be a toll call)
• The middle digit could only be a 0 or 1 (0 for states and provinces with only one Area Code, and 1 for states and provinces with more than one). This restriction allowed an Area Code to be distinguished from an exchange (an exchange, the equipment that switched up to 10,000 telephone numbers, was denoted at that time by the first two letters of a word and one number; today exchanges are denoted by three digits).
• The last two digits could not be the same (numbers of the form \(abb\) are more easily remembered and therefore more valuable)—thus \(x\)11 dialing sequences such as 911 (emergency), 411 (directory assistance), and 611 (repair service) for local services were protected. This also permitted the later adoption of 500 (follow-me), 600 (Canadian wireless), 700 (interconnect services), 800 (toll-free calls), and 900 (added-value information services).

As a result only 144 Area Codes were possible. Initially 86 were used and were assigned so that numbers more rapidly dialed on rotary dials went to districts with larger incoming traffic (e.g., 212 for Manhattan). The remaining 58 codes were reserved for later assignment.

This pool of 58 new Area Codes was sufficient for more than four decades. Finally, when more than 144 Area Codes were needed, new Area Codes were created by relaxing the restriction that the middle digit be only 0 or 1. On January 15, 1995, the first Area Code with a middle digit other than 0 or 1 was put into service, in Alabama. The present restrictions on area codes are that the first digit cannot be 0 or 1, the middle digit cannot be 9, and the last two digits cannot be the same. As of the beginning of 2000, 108 new Area Codes had been started, this great demand due in part to expanded use of the telephone networks for other services such as fax and cell phones, in part to political pressure from jurisdictions such as the Caribbean islands that wanted their own area codes, and in part by the large number of new telephone companies offering service and therefore needing at least one entire exchange in every rate billing district. Some people believe that the North American Numbering Plan (NANP) will run out of area codes before 2025, and there are various proposals for how to deal with that.

The transition in 1995 went remarkably smoothly, considering that every telephone exchange in North America required upgrading, both in revised software and, in some cases, new hardware. By and large the public was not aware of the significance of the change. This was a result of the generally high quality of North American telephone service, and the fact that the industry was tightly coordinated. The only glitches seem to have been that a few PBX (Private Branch eXchanges) designed by independent suppliers were not upgraded in time. Since 1995 the telecommunications industry in North America has changed greatly: it now has less central control, much more competition, and a much wider variety of services offered. Future changes in the numbering plan will surely result in much greater turmoil and inconvenience to the public.