I'm taking the GSM plunge based on the build-out they've done just recently in Texas. Looked at their GSM map as well as confirming with AT&T rep that Stillwater has GSM coverage. Of course it may only be by OSU but we'll see in a couple weeks...
GSM is where all the new towers are going up and it has the best rate plans, including unlimited free mobile-to-mobile. In addition, Cingular -- who's buying ATTWS -- is also GSM, so the direction is clear with the combination of the two.