<P> North American area codes 240 and 301 are telephone area codes for the western half of Maryland . They serve Maryland's portion of the Greater Washington, D.C., metro area, portions of southern Maryland, and the more rural areas in the western portion of the state . This includes the communities of Cumberland, Frederick, Hagerstown, Gaithersburg, Rockville, Landover and Silver Spring . </P> <P> The main area code, 301, was one of the original area codes established in 1947, and originally covered the entire state of Maryland . This was despite the fact that, then as now, the bulk of the state's population is split between two very large metropolitan areas--Baltimore and the Washington suburbs . From 1947 to 1990, it was possible for telephone users on the Maryland side of the Washington metropolitan area to dial any number in the region with only seven digits . Although the metro area was split between three area codes--the district's 202, Northern Virginia's 703, and Maryland's 301--it was a single local calling area . Every number on the Maryland and Virginia sides of the metro was given a "hidden" number in the District's 202, essentially using 202 for the entire metro . One consequence of this was that no central office codes could be duplicated in the D.C. area . For instance, if 202 - 574 was in use in the District or 703 - 574 was being used in Northern Virginia, the corresponding 301 - 574 exchange in Maryland could only be used in areas at a safe distance from the Washington metro area, such as the Eastern Shore . By the end of the 1980s, the D.C. area was running out of prefixes . To free up available numbers, the suburban use of 202 was ended in 1990 . </P>

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