Need help, I want to put this phone on ATT or Tmobile.

This is where I stand:

-Iphone 3GS 3.1.3 Firmware 5.12.01 bb ( heard not JB or unlock yet ) I'll wait..hopefully. And will try to put an ATT prepaid plan in the meantime.

-LOOKING FOR NO CONTRACTS, to people that have no contract plans answer the following please.

-Heard ATT prepaid plan works on iphone, unlimited call and text, but they cant "guaranteed" 3g will work, or any data plans,supposedly only contract plans, is this true?
-Does anybody with ATT prepaid, have 3g working? Do I need to put the 3g service then add an APN?
-Would consider Tmobile but their 3g dont work with iphone or something.

Please answer this at your earliest convenience, thank you all.