Originally the telephone exchanges, as everywhere else, were manual. The precise details of the intermediate stages before adopting the generally standard 2-letter, 5-digit pattern are unknown to me, except that it is likely that the Washington, D. C. 2-letter, 4-digit early dialing pattern was implemented at some point. At present, I have no information on this area except from one telephone directory toward the end of the period of 2-letter, 5-digit numbers, so that only that part of the late dialing period is tabulated here. This will be expanded as information becomes available to me.
Other regional tables:
|The Baltimore-Washington region|
|Baltimore, Md. (city)||Baltimore, Md. (suburban)||Washington, D. C. (city)||Washington (Maryland suburban)||Washington (Virginia suburban)|
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Last modified February 19, 2015.