So, you are enjoying the new iOS 4 and also expecting to get hands on on dazzling iPhone 4. They both make a handsome combination of hardware and software. There may be one thing which you are missing is the freedom to use iPhone any carrier other than AT&T. These carriers may be Tmobile or any other iPhone compatible network in the world.
Your wish comes true as iPhone Dev Team have released ultrasn0w to unlock iOS 4 on iPhone 3GS 3G. ultrasn0w 0.93 uses the same exploit found by Sherif Hashim to unlock iPhone 3.1.3 [05.12.01] which remains vulnerable in 05.13.04 baseband for iOS 4.