The only remaining prefixes could not be assigned without breaking seven-digit dialing in the region, leading C&P to terminate the central office code protection scheme in order to make additional prefixes available for use. Conversely, if a 1-703-552 number was in use in Northern Virginia or a 1-301-552 Maryland suburbs, the corresponding 1-202-552 number could not be used in the District.īy Spring 1990, C&P Telephone (later part of Bell Atlantic and now Verizon), the Regional Bell Operating Company for the District, advised the North American Numbering Plan Administrator (NANPA) that the last interchangeable central office code in the area would be assigned in the second half of the year. If a 1-202-574 number was in use in the District, the corresponding 1-703-574 number or 1-301-574 number could only be assigned to jurisdictions a safe distance from the metropolitan area, such as southwestern Virginia or the Eastern Shore of Maryland. This scheme was implemented via a system of central office code protection, in which central offices in the three numbering plan areas could not duplicate any central office prefixes for any of the three area codes in the WMEA. The entire WMEA was reachable via long-distance services by dialing area code 202, for which purpose AT&T Long Lines had established cross-referenced operator routing codes for all affected central offices. From the 1950s to 1990, it was possible to complete local calls in the WMEA with only seven digits.
This is despite the fact that the WMEA was split between three numbering plan areas (NPAs): the District's 202, 301 in southern Maryland, and 703 in Northern Virginia.
Since the creation of the North American Numbering Plan (NANP) in 1947, most of the inner ring of the Washington metropolitan area has been a single local calling area, the Washington Metropolitan Exchange Area (WMEA).
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