Southeastern Pennsylvania was assigned the 215 area code in 1947 when the North American Numbering Plan of the "Bell System" went into effect. The geographic area covered by the code was split nearly in half in 1994 when area code 610 was created, with the city and its northern suburbs retaining 215. Overlay area code 267 was added to the 215 service area in 1997, and 484 was added to the 610 area in 1999. A plan in 2001 to introduce a third overlay code to both service areas (area code 445 to 215, area code 835 to 610) was delayed and later rescinded.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): What area code is used in Philadelphia in 1947?
215