As I remember Tennessee's rules, the PSC requirement was that every adjacent county was to be considered local.
Area codes could usually cover multiple counties, but you usually know what city your calling destination is in. With ISP dial-in numbers, you might not, but that's pretty much the exception.
Exchange boundaries rarely match municipal boundaries, and there are a whole bunch of arcane special cases like the one in Vermont that a call to your town hall must be local. That's why it would be nice to be able to query the billing database that really knows. Regards, John Levine, johnl@iecc.com, Primary Perpetrator of "The Internet for Dummies", Information Superhighwayman wanna-be, http://iecc.com/johnl, Mayor "I dropped the toothpaste", said Tom, crestfallenly.