Quoting Henry Baker <hbaker1@pipeline.com>:
On the other hand, phone area codes seem to have been chosen with some sort of "coding theory" algorithm, so that points close to one another would have area codes as different as possible.
To understand area codes you need to know about real old-style dial phones. They optimized the time it took to dial the high population area codes. New York was 212; Los Angeles 213. States with more than one area code had codes with a "1" as the central digit. States with only a single code used a zero. Three digit codes ending in zero were avoided as exchange codes for many years, on the assumption that they would be required as area codes eventually. They were used intially as additional area codes, but there were far too few of them, so area codes with any three digits came into use a few years ago.