<P> Area code 305 is the area code for all of Miami, Florida, Miami - Dade County, and the part of Monroe County in the Florida Keys in the United States . The mainland portion of Monroe County is served by area code 239 . The numbering plan area 305 was overlaid by area code 786 in 1998 . </P> <P> Area code 305 was one of the original area codes created in 1947, and originally covered the entire state of Florida . The western part of the peninsula from the Tampa Bay area south, which was served mostly by GTE (now part of Verizon), was separated into area code 813 in 1953 . As a result of the increase in the state's population, North Florida from the Panhandle to Jacksonville was assigned area code 904 with a permissive dialing period beginning July 6, 1965, and a mandatory dialing period beginning January 1, 1966 . </P>

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