Area codes 410, 443, and 667

In 1947, the American Telephone and Telegraph Company (AT&T) published the first configuration of a nationwide telephone numbering plan for Operator Toll Dialing, which designated the state of Maryland as a numbering plan area and assigned area code 301.

By the late 1980s, the rapid growth of the Baltimore and Washington suburbs, as well as the proliferation of fax machines and pagers placed the numbering resources in the danger of exhaustion of central office prefixes.

On the other side of the Potomac River, many of the same factors resulted in most of the old 703 territory outside of Northern Virginia split off as area code 540 in 1995.

Area code 410 officially entered service on October 6, 1991; it was initially implemented in a permissive-dialing phase, with ten-digit dialing for local calls across the new 301/410 boundary.

[4] Although the split was intended to be a long-term solution, within five years 410 was already close to exhaustion due to the proliferation of cell phones and pagers, particularly in and around Baltimore.

However, the alternative would have been a split that would have forced residents of either Baltimore or the Eastern Shore to change their numbers for the second time in a decade.