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.
You can unlock iOS 4 on iPhone 3GS 3G if you abide by the tutorial.
Function 1: Your iPhone 3GS 3G should be running on jailbroken iOS 4. If this is not the case, you can jailbreak it using redsn0w 0.9.5.
Function 2: Run Cydia on jailbroken iPhone and then navigate to “Manage” tab at bottom.
Function 3: Touch “Edit” and then “Add”. You will be asked to enter a URL for repository source. Enter “http://repo666.ultrasn0w.com” and finally “Add The Source”. Leave the rest for Cydia as it will update the sources.
Function 4: Now search “ultrasn0w” in Cydia and install the application. The latest version of ultrasn0w would be 0.93. ultrasn0w 0.93 will unlock iOS 4 on iPhone 3GS 3G.
Function 5: Restart iPhone 3GS 3G and you can use iPhone with any carrier.