As promised by the iPhone Dev Team and MuscleNerd, Ultrasn0w 4.3.1 unlock, new version of Ultrasn0w is available to support iOS 4.3.1. It is basically a fix and is developed by msft_guy and iH8sn0w. Previously Ultrasn0w 1.2 unlock was broken on the iOS 4.3.1 firmware. That means 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.
Remember the Ultrsn0w 4.3.1 unlock is compatible with devices running iOS 4.3.1 firmware. Its WILL NOT unlock higher basebands whose unlock is not possible right now. But it will continue to unlock the old ones. You can say that its just a new version of Ultrasn0w for people who have upgraded to iOS 4.3 and also jailbroken it using PwnageTool 4.3 or Sn0wbreeze 2.5. If you are still confuded, it will ONLY be compatible with basebands which includes 01.59.00 / 04.26.08 / 05.11.07 / 05.12.01 / 05.13.04 / 06.15.00.
How To Unlock iOS 4,3.1 iPhone 4 3GS With Ultrasn0w Fixer [How To Guide]
UPDATE: Those who are still facing issues after using Ultrasn0w Fixer, iPhone Dev Team has updated:
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