I've seen one website that had slightly varying rates for different area codes in USA, but can't remember where it was, and I don't think there were exchanges listed within area codes. I expect those Iowa numbers were a bit higher.
Some of the Betamax VoIP companies say they have differing retail rates, but their wholesale arm VoiceTrading has the same for both
http://backsla.sh/betamax
- but as I suggest, how likely is it they would bother to look up a table with over 130,000 elements?