The area code was one of the original NANP area codes established in October 1947 by AT&T. After the State of New Jersey with area code 201, the District of Columbia was the second numbering plan area (NPA). An NPA that comprises an entire state received a code in which the second digit was '0'.
According to the most recent projections from the North American Numbering Plan Administrator, 202 is projected to exhaust by late 2022. Since August 3, 2020, interim jeopardy procedures are in effect that limit new office code assignments to three per month. Each operating company may only file for three applications per month.
In October 2020, the North American Numbering Plan Administrator issued a planning letter for the addition of area code 771 to numbering plan area 202, creating an all-services overlay for the District of Columbia. Permissive ten-digit dialing is scheduled for a six-month period starting April 10, 2021. The earliest central office code activation is scheduled for November 9, 2021.
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). This is despite the fact that the WMEA spills into three numbering plan areas (NPAs): the District's 202, 301 in southern Maryland, and 703 in Northern Virginia. From the 1950s to 1990, it was possible to complete local calls in the WMEA with only seven digits. 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. 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.  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. Conversely, if a number was in use in the Virginia or Maryland suburbs, it could not be used in the District.
By 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. 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. This change was implemented in a permissive dialing period from April 1, 1990 to October 1, 1990, at which time all home-NPA (HNPA) local calls maintained seven-digit dialing; all HNPA direct-dialed toll calls, required 1 and ten-digits; foreign-NPA (FNPA) local calls were dialed with just the ten-digit number; FNPA direct dialed calls required dialing 1 and ten-digits. Operator-assisted calls were all dialed as 0 and ten-digits.
Although the end of central office code protection was intended to prevent area code splits, it did not provide enough relief to meet demand on either side of the Potomac River. In Maryland, the removal of code protection was successful for only a few months. By the end of 1990, the Chesapeake and Potomac Telephone Company of Maryland filed to assign area code 410 to Baltimore and the eastern half of Maryland, effective October 5, 1991. In Virginia, the delay amounted to six years, until 1996, when area code 540 was installed and permissive dialing ended January 27, 1996.
The region's continued growth in the 1990s ultimately led to both suburban area codes being overlaid, with area code 240 overlaying 301 in 1997, and area code 571 overlaying 703 in 2000.
With 202 facing exhaustion in late 2022, the North American Numbering Plan Administrator announced in October 2020 that area code 771 would be added to the numbering plan area of the District of Columbia. The Public Service Commission of the District of Columbia approved a plan to phase in the new area code over a 13-month period. When area code 771 becomes active, all calls made from the District of Columbia are required to include the area code. 202 had been one of the few urbanized area codes without an overlay, making Washington one of the largest cities where seven-digit dialing was still possible. The implementation of 771 will break seven-digit dialing for calls within the District.
Even with the implementation of ten-digit dialing in the Washington metro, much of the Washington area is a toll-free calling zone–one of the largest in the eastern United States, covering large slices of northern Virginia and southern Maryland.
Areas such as Alexandria, Arlington, Fairfax, Falls Church, McLean and Tysons in Virginia (703/571) and Rockville, Gaithersburg, Upper Marlboro, Bethesda and Landover in Maryland (301/240) are a local call to Washington.
- AT&T, Notes on Nationwide Dialing (1955)
- 2020-1 NRUF and NPA Exhaust Analysis
- NANPA NPA 202 (District Of Columbia) Interim Jeopardy Procedures 2020-08-03
- NANPA Planning Letter No. 547 (October 22, 2020)
- Barnes, Sophie (2020-09-22). "DC Reveals Its Next Generation Area Code: 771". NBCWashington.com. WRC-TV.
- AT&T Long Lines, Distance Dialing Reference Guide (1974-04-01)
- NANPA Bellcore Information Letter IL-90/04-003
- NANPA, Bellcore Information Letter IL-90/12-049
- NANPA, Bellcore Information Letter IL-95/04-007
- NANPA Administration System: Area Code 202 Archived 2009-01-29 at the Wayback Machine
- Local calling guide: Washington Zone 1, DC
- Local calling guide: Washington Zone 8, VA
- Local calling guide: Washington Zone 19, VA
- Local calling guide: Washington Zone 17, VA
- Local calling guide: Washington Zone 10, MD
- Local calling guide: Gaithersburg, MD
- Local calling guide: Washington Zone 15, MD
- Local calling guide: Washington Zone 2, MD
- Local calling guide: Washington Zone 4, MD
|West: 571/703||area code 202||East: 240/301|
|Maryland area codes: 240/301, 410/443/667|
|Virginia area codes: 276, 434, 540, 571/703, 757/948, 804|