<Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (December 2009) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (December 2009) (Learn how and when to remove this template message) </Td> </Tr> <P> In the United States and Canada, ten - digit dialing is the practice of including the area code of a telephone number when dialing to initiate a telephone call . When necessary, a ten - digit number may be prefixed with the trunk code 1, which is often referred to as 11 - digit dialing or national format . </P>

When did you have to start using area codes