I have an old map of Oklahoma City from the early 1960s, and for phone numbers, they use two letters and 5 numbers ex: VI 3-6182. I was curious if anyone could give me some insight as to what the letters stand for? I that they stand for numbers and I do know that the VI stands for Victor (My mom grew up around Hefner and May and her phone number began with Victor.) Possibly a list of the abbreviations? Any information or insight on this would be greatly appreciated.