Remember in
old movies, where somebody would pick up the
telephone and say, "
Operator, I need
Oxford-50456"? Oxford was the name of the local telephone exchange (or Bell
central office), represented on your telephone by its first two letters: OX, or 69. So, the
modern number would be 695-0456. This is why in a particular area, most
phone numbers historically began with the same two
digits.
Telco employees still refer to central offices by these names. Incidentally, "Oxford" is the CO in downtown Vancouver, WA, where many phone numbers have the prefix "69x".