I'm in NC too and have experienced the same thing you have. Once I leave my city I don't come across another 4G area for a two hour drive. It's only painfully slow EDGE. When I'm in the far western part of the state I roam on AT&T and it's on their EDGE network.

In all the T-Mobile EDGE areas I travel to AT&T has those same ares covered with 4G. T-Mobile's maps are a farce and do not accurately portray how little 4G coverage they have. However, I'm not confident at all that T-Mobile will ever improve coverage in these areas. They seem to be a company that's interested in chasing the latest fad. When everybody was building out 3G they were late to jump on the bandwagon. But before they got 3G built out, they stopped and jumped on the 4G bandwagon. Now they're abandoning completing their HSPA+ 4G network to start building out LTE.

If you live in a large major metro area you'll be the recipient of their latest project. But if you live anywhere else you're going to be stuck on EDGE because they'll never get to you as they keep starting over before they've completed building out their current network.

As soon as my contract is up I'll be going back to AT&T. The few pennies I save with T-Horrible doesn't justify the poor coverage.