It is interesting to look at the distribution of the 'old' area codes i.e. the ones with second digits of 1 or 0.
Not only can you tell which places were important by having fast-dialling codes like 212 - New York and 213 - Los Angeles, but also which places were not important - the ones with slow-dialling zeros in their codes, for example Colorado, Wyoming, Montana, Nebraska and the Western Canadian provinces.