If you order an unlocked iPhone 4S via Apple, you will get an absolutely unlocked phone that doesn't require any tweaking for it to work on T-mobile. Getting a prepaid monthly plan at a T-mobile store or in your case, at Wal-mart, won't cost you an arm or a finger, just about $30 Just tell them you need a micro-sim and everything is all set (not sure if they will charge you $20 extra for the microsim....) But you need the service and sim card in order to activate your phone. Just a reminder, if you really don't mind EDGE network, no MMS, no Visual Voicemail, and No "gps mapping," I think about $800 is all you need lol.
Thanks for the response. No, I don't mind EDGE for now as I will be on wi-fi most of the time anyway. From what I have read elsewhere the 4S is pretty much good to go out of the box with the addition of the Tmo micro-sim. It also appears that a fix for MMS is working as well. And, yeah, Visual VM I can do without. Thanks again.