In October 1990, calls CROSSING the Potomoc (i.e., between DC/202 and northern VA/703, as well as between MD/301 and northern VA/703), also crossing the DC/202 northern VA/703 boundary became mandatory ten-digits. It is still a local (not toll) call, but almost twenty years ago, it became mandatory ten-digits.
About a year later, in Fall 1991, Maryland had an area code split, the Baltimore/eastern part changing to 410, while the western part including the suburbs of DC retained 301.
In 1995, 703 was split (again, the earlier split of 703 was in June 1973 when the entire state's 703 was split with 804 for southeastern VA), the new area code being 540, shrinking 703 down to just the extended northern VA suburbs of DC.
In Summer 1997, the entire state of Maryland became mandatory ten-digit dialing for local calls. 301 was overlaid with 240; 410 was overlaid with
443. There are two pending further overlays, but the implementation dates are still TBD -- 301/240/(227) and 410/443/(667).In March 2000, 703 for the extended northern VA suburbs of VA was overlaid with 571, along with mandatory ten-digit local dialing.
SO, presently the ONLY 7D local dialing allowed in the Washington DC metro area is for calls STRICTLY WITHIN 202/DC itself. ALL other local calls, within the MD sub, within the VA sub, and between any of the three (MD, VA, DC) are mandatory ten-digits, although still local (not toll).
Intra-202/DC dialing is PERMISSIVE 10-digits, but 7-digits still works but only for that limited region.
It will still be a few years before 202/DC needs relief. But I seriously doubt that Verizon, the wireless providers, and the CLECs would propose a split of 202/DC. Expect that 202/DC will be overlaid at that time, and the currently permissive 10-digit intra-202/DC local dialing will become mandatory, and thus no more 7-digit intra-202/DC local dialing.
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