PhoneSouth- and Central Western Pennsylvanians will have to get used to a third area code soon. The Pennsylvania Public Utilities Commission will soon activate area code 878. The new code was announced in 2001, but its activation was delayed due to a number conservancy program. It will serve as an overlay in the 412/724 region. It will go into use for all new numbers in the larger 724 region first, because nearly all of those numbers are taken. It will do the same in 412 once all of those numbers are exhausted.. 

412 is one of the country’s original area codes and has served Southwestern Pennsylvania since 1947. When 724 went into effect, 412 became and remains limited to the majority of Allegheny County.

724 was announced in 1997 and was activated in 1998 as a “replacement” code for the region outside of Allegheny County. Originally 724 was proposed as an overlay but instead became a replacement in extreme northern and eastern Allegheny County; parts of  Clarion, Crawford  and Venango Counties; most of Indiana, Mercer and Westmoreland Counties; and all of Beaver, Butler, Fayette, Greene, Lawrence and Washington Counties.