The iOS 4.3 jailbreak is out now and you could also unlock your iPhone 4 running iOS 4.3 if you have upgraded to it without updating the baseband. Tools like PwnageTool on Mac or Sn0wbreeze on Windows helps you to update your iPhone 4 to iOS 4.3 without upgrading the baseband so that you could unlock it using earlier version of Ultrasn0w.
NOTE: Take your time and read the complete jailbreak and unlock process carefully before attempting it. And I am mentioning once more, Ultrasn0w 1.2 works only for those having iPhone 4 on 1.59.xx baseband.
Steps to unlock iPhone 4 4.3 iOS
1. Jailbreak iPhone 4 4.3 iOS without upgrading the baseband.
2. Now open up Cydia to unlock iPhone 4 4.3 iOS.
3. Choose the ” Manage ” tab at the bottom.
4. Choose the ” Sources ” option.
5. Tap the ” Edit ” button and then on the ” Add ” button.
6. Then add the source ” http://repo666.ultrasn0w.com “.
7. After it is added, search for ” ultrasn0w 1.2 ” in Cydia.
8. Now, install the Ultrasn0w 1.2 app to unlock iPhone 4 4.3 iOS.
That’s it! You’have done it!