Finally its here. But, its not official. @iH8Sn0w, @Msft_guy & @DjayB6 has worked on Ultrasn0w fixer to make Ultrasn0w compatible with iPhone 3GS & iPhone 4 running iOS 4.3.1.
Ultrasn0w Fixer does the job of Unlocking your iPhone. But, there is a minor bug – You will notice a Single Signal Bar in the status bar, even if you have full signals.
For those, you are not comfortable using Ultrasn0w Fixer, you can still wait for the iPhone Dev Team to release an updated version of Ultrasn0w. Untill then, stay tuned.. Rest of you can follow the below instructions..
What is Ultrasn0w Fixers: It only make the official Ultrasn0w Unlock Tool compatible with iOS 4.3.1. It doesn’t unlock any new baseband’s. Currently Ultrasn0w is only supports the following baseband (04.26.08, 05.11.07, 05.12.01, 05.13.04, 06.15.00, and 01.59.00))
Step 1: Jailbreak Your iPhone 4 / iPhone 3GS using any of these guides (RedSn0w 0.9.6rc9 / PwnageTool 4.3 / Sn0wbreeze 2.5)How To Unlock iPhone 4 / iPhone 3GS Running iOS 4.3.1 Using UltraSn0w Fixer
Step 2: Launch Cydia >> Manage >> Source >> Edit >> Add >> Type the following source >> Add Source
http://cydia.pushfix.info/Step 3: Once the Source is verified and updated, Tap on Done & Tap on the Added Source
Step 4: Now, Look for Ultrasn0w Fixer
Step 5: Select It, Tap on Install >> Tap on Confirm to complete the installation
Note: This will automatically install Ultrasn0w on your iPhone 4/ iPhone 3GS
That’s it! Give your iPhone a reboot and enjoy.