Does anyone know where I can find a basic (and preferably free) listing of which area codes are local to which other area codes? We're looking at tail-end hopoff and I can't find a good listing of which area codes besides the explicit ones to route out remote gateways (for example, I know a call to 913 from Nevada should be routed out the Kansas City router, but 816 is also local and should also be sent out the KC router).

Thanks,

Jim