GSM question

[sndtubes]

I'm unfamiliar with GSM and had a hypothetical question. IF we are able to get our Sprint TP2's operating on USA GSM networks such as AT&T, will our Sprint phones roam onto those towers without a roaming charge?? I would assume that Sprint does not have a roaming agreement with Sprint or any other CDMA carrier for that matter. Am I all wet? Or is the phone only going to function on a USA GSM tower only if you have an AT&T account with an AT&T sim card installed? Forgive me for my ignorance y'all. It would be sweet if we can roam onto an AT&T tower as the Sprint signal at my house SUCKS (almost useless) and AT&T just put a new tower up 1/10 mile from my house . Thanks