I have ATnT....which merged with cingular???

Anyway they use different technology than Sprint so you can't roam onto Sprint's towers. Being out in the sticks, most important thing for me was coverage.....with Sprint it was bad and non-existant in some areas, like my house

with ATnT I can get a signal if I stand out in the yard, on one foot holding a coathanger wrapped with tinfoil.....IP's right about the lowend phones (you'd be surprised how much better a phone you get if you spend $50 vs. $0, with rebates and whatnot mine was a $200 Motorola) and about Sprint, but you gotta check coverage, physically if they'll let you take the phone.
Whenever Dunbarton allows a tower....big battle over it in the past, both Sprint and ATnT have plans to hook up to it. The town's basically PO'd cause the best site for the tower is in some guy's backyard, not public property, so they wouldn't get the 25-year rental contract monies and now they're trying to figure out a way to tax it out of someone before they'll let the tower in