Telephone Numbers in The United States - Expansion - Splits and Overlays

Splits and Overlays

By 1995, many cities in the United States and Canada had more than one area code, either through splitting the city into different areas (splits) or having more than one code for the same area (overlays). For example, in Manhattan, subscribers' numbers had the NPA code 212, but two additional codes—first 917 (which initially was exclusively for cellular phones and pagers until that idea was struck down in a Federal court), then 646—were also introduced. This means that the area code must be dialed, even for local calls. In other areas, 10-digit or 11-digit dialing is now required for all local calls. The transition to 10-digit dialing typically starts with a permissive dialing phase in which both 7-digit and 10-digit dialing is optional. During this period, the transition is heavily publicized. After a period of several months, the mandatory dialing phase is introduced, in which 7-digit dialing no longer works. Atlanta was the first US city to have mandatory 10-digit dialing throughout its metropolitan area, roughly coinciding with the 1996 Summer Olympics held there. Atlanta was used as the test case not only because of its size, but also because it enjoyed the world's largest fiber optic network at the time (five times that of New York then), and it was home to BellSouth (now part of AT&T), then the Southeastern Regional Bell Operating Company.

• 7-digit dialing: NXX xxxx (NPA code not required)
• 10-digit dialing: NPA NXX xxxx
• 11-digit dialing: 1 NPA NXX xxxx (1 is the NANP trunk prefix for long distance circuits).

The overlap between area codes and exchange prefixes has occasionally produced some confusion because the three digits can be the same for both. Nashua, New Hampshire, for example, has a local exchange code, (603) 888. 888 is also an area code for toll-free calls. If somebody in Nashua means to call 1-888-555-1212, but forgets the trunk prefix 1, he or she will actually dial the local number 603-888-5551. This, however, is generally not a problem in major metropolitan areas with overlapping area codes, which were mandated by the FCC to dial all ten digits for all local calls so as not to give new numbers or telecommunications providers a disadvantage.