proliferation of cell phones and pagers, so that further relief became necessary. By this time, overlays had gained more acceptance, so area code 878 was implemented as an overlay for both 412 and 724 on August 17, 2001. Although telephone numbers were not assigned for 878 until 2013 (and were only assigned in the 724 area until 2015), ten-digit dialing has been mandatory across southwestern Pennsylvania since 2001.

Service area

The numbering plan area includes Allegheny county, with the

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