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.