kat, the song is actually "PEnnsylvania 6-5000", not "500" -- still only two letters in the name. The US might have used the British 3-letter system very early on, but I think that after the 7-digit phone numbers were standardized, two letters and a number were used to identify exchanges all across the country. In northeast Philadelphia our number was DEvonshire 2-9220 (now there's a nice bucolic name for you!). My neighbors and relatives tended to be DE3 or DE8, or else FIdelity 2, MAyfair 4, PIoneer 4, PIlgrim 2 (same "PI" but a different name), while friends in other parts of the city had CHestnut Hill 7, PEnnypacker 5, HObart 4, GArfield 7, DAvenport 9, WIndsor 2--and my memory fails me beyond that. As I recall, the changeover to using 7 digits occurred sometime around 1969 or 1970. The old phone dials didn't have letters by the number "1", and there was no "Q" or "Z", so 7 was "PRS" and 9 was "WXY". Here's a tricky question: what letter(s) would you find next to the number "0"?

Aloha,
Mark