dsphil1338 -
I have AT&T and have used that service provider for some time now. My experience has been the further south and east you travel from McAlester the spottier the cell coverage. You will be pretty much on the edge of coverage with AT&T particularly in the mountainous areas of the state. As an example, when traveling from Big Mac to Talihina, you loose cell coverage just east of Hartshorne, pick it up reasonably well about two miles out of Talihina, that is a huge gap in service if you need it.

Sometimes you will connect to another service provider in the southeast area known as "Pine Cellular".
Traveling from Talihina toward the east is fair since the local area cell tower's antennas are directed toward the east. Dropping to the south along hwy 259 traveling toward Broken Bow is spotty again and you usually cannot pick up a signal until entering the Smithville area.
Other people may have better results than I if they are using another service provider. Traveling along the main transportation corridors like the turnpikes you should expect uninterrupted service.