Folsom, Gap, Hamburg, Havertown, Kutztown, Lehighton, Macungie, Malvern, Media, Newtown Square, North Catasauqua, Northampton, Oxford, Palmerton, Paoli, Pottstown, Reading, Shillington, Sinking Spring, Tamaqua, Upper Darby, West Chester, Whitehall Township, Willistown, Wind Gap, Wyomissing. Prior usage for TWX Most of the N10 area codes (510, 710, 810, and 910) were used prior to 1981 by AT&T for the Teletypewriter Exchange Service (TWX). Telex use of these area codes in the United States was decommissioned in 1981 when Western Union, who had acquired the TWX network in 1969, and renamed it Telex II, upgraded the network to "4-row" ASCII operation. Area code 510 was reassigned to Oakland, California in 1991, 710 went to the US federal government in 1983, 810 and 910 were assigned to Michigan and North Carolina, respectively in 1993. The last TWX code, 610, outlived the others because it was controlled by Bell Canada, and not directly affected by AT&T's exit from teletype services. Area code 610 was replaced with non-geographic Canadian area code 600 in 1992, freeing the area code for reassignment to general telecommunication services. When it was reassigned in 1994, area code 610 was the last geographic area code assigned to follow the original pattern of having the digits 1 or 0 in the middle position. In 1995, the assignment of interchangeable NPA codes commenced, which broke the pattern. See also List of NANP area codes List of Pennsylvania area codes References External links North American Numbering Plan Administration 610 and 484 610 and 484 Berks County, Pennsylvania Bucks County, Pennsylvania Carbon County, Pennsylvania Chester County, Pennsylvania Delaware County, Pennsylvania Lancaster County, Pennsylvania Lehigh County, Pennsylvania Monroe County, Pennsylvania Montgomery County, Pennsylvania Northampton County, Pennsylvania Schuylkill County, Pennsylvania Telecommunications-related introductions in 1994 Telecommunications-related introductions in 1999