npl@spuxll.UUCP (07/15/84)
Having seen some old Telco drawings, etc. for Central Offices, I can state that, at least in NYC, the exchanges were originally 2 characters, followed by 4 digits. (Phone numbers for the Chief Engr. etc, were listed as AUdobon 1234, or AU-1234. The following is conjecture, but stands to reason that as phone service was getting to be more and more prevalent, the Telco went from just a string fo 4 digits to a mnemonic identifying the area of the city (local countryside) plus four digits. As more and more people subscribed to phone service, some exchanges had to grow past 9999 customers. The fast solution was to add a seventh digit. e.g. CHelsea became CHelsea-2 and CHelsea-3, -4, -5, etc. Other than the clue from the old drawings, I have nothing to back the above other than extrapolation. Nick Landsberg