Area codes 610 and 484

Area codes 610 and 484 are telephone area codes which serve the eastern and southeastern regions of Pennsylvania. The area includes areas to the west of Philadelphia, along with the cities of Allentown, Bethlehem, and Reading. It includes much of the Delaware Valley, including almost all of Delaware County and most of the Philadelphia Main Line.

Created in anticipation of number exhaustion in the area code 215 serving the whole of southeastern Pennsylvania, area code 610 was split off on the morning of January 8, 1994, with a year-long permissive dialing period ending on the morning of January 7, 1995. It was Pennsylvania's first new area code since the implementation of the area code system in 1947.

Three exchanges which would have switched to 610 were instead switched to 717, the area code for most of the eastern half of the state outside of the Delaware and Lehigh Valleys. They were 267 at Denver, 445 at Terre Hill, and 484 at Adamstown, with 267 being replaced by 717-336 because 717-267 was already in use at Chambersburg. These exchanges were all served by non-Bell telephone companies which sought to consolidate their eastern Pennsylvania customers into one area code, and would have had to change area codes anyway.

Further growth in the region over the subsequent five years spurred the introduction of overlay plans in the Commonwealth, with area code 484 being overlaid upon 610 on June 5, 1999, along with the introduction of mandatory ten-digit dialing. The implementation of 484 was hastened because the entire state of Delaware is part of the Philadelphia LATA, meaning several exchanges in Delaware's 302 weren't available for use.

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