Area code 410

Area codes 410, 443, and 667 are telephone area codes serving the eastern half of the U.S. state of Maryland, including the Baltimore metropolitan area and the Eastern Shore. The 410 area code is the main area code, while the 443 and 667 codes are overlay codes. 443 and 667 were primarily used with cell phones and CLEC carriers such as Comcast or Cavalier Telephone when introduced but have since become universal in their carrier availability.

Before these area codes were created, all of Maryland had been served by 301 since the institution of area codes in 1947, even though the state is home to two very large metropolitan areas--Baltimore and Washington, D. C. This made Maryland one of the most-populous states to be served by a single area code. However, by the late 1980s, 301 was on the verge of exhaustion due to the rapid growth of the Baltimore and Washington suburbs. The supply of available numbers was further limited by the fact that most of the Maryland side of the Washington area shares an LATA with northern Virginia and the District itself. For over 40 years, it was possible to make a call between portions of the Washington area with only seven digits, since every number in 301 and northern Virginia's 703 was given a "hidden" number in the District's area code 202.

Plans had already been underway to break this longstanding scheme, but it soon became apparent that this would not free up enough numbers to keep up with demand. It was now obvious that a second area code was necessary. In 1991, state officials came up with a plan to add a second area code, the 410 code, to the state. They eventually decided that the Baltimore metropolitan area and the Eastern Shore would get the new area code, while western and southern Maryland—including the Washington suburbs—would remain with the 301 area code.

Area code 410 officially entered service on October 6, 1991; it was initially implemented in permissive-dialing mode, not as a flash-cut, with the 10-digit dialing scheme coming in for local calls across the new 301/410 boundary. The split largely followed metro lines. However, part of Howard County stayed in 301. While Howard County is reckoned as part of the Baltimore area, some areas in the southern part of the county identify more with Washington.

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