Ultrasn0w fixer for iOS 4.3.1 unlock on iPhone 4 and iPhone 3GS on older basebands. The fix is developed by msft_guy and iH8sn0w.
How to Guide To Use Ultrasn0w fixer for iOS 4.3.1 to Unlock iPhone 4 and 3GS: Step 4: Now press “Done”. Step 5: Now select ”Pushfix.info” to Install it. Step 6: Once its done with installation. Go to Pushfix.info. Scroll down to find “Ultrasn0w fixer for 4.3.1”. Select and to install the package. After that it will restart your device. Your device is now unlocked on iOS 4.3.1 on basebands 01.59.00 / 04.26.08 / 05.11.07 / 05.12.01 / 05.13.04 / 06.15.00. DO NOT use it other than the mentioned basebands.
Ultrasn0w was previously unable to unlock iPhone 4 and 3GS devices after untethered iOS 4.3.1 jailbreak. But now you can use Ultrasn0w 4.3.1 fixer to unlock your device. DO NOT take it as a new unlock tool, it can ONLY UNLOCK basebands 01.59.00 / 04.26.08 / 05.11.07 / 05.12.01 / 05.13.04 / 06.15.00.