Finally, Dev-Team had released the untethered jailbreak for iOS 4.3.1 on all iOS devices from iPhone to iPad(except iPad 2) their next objective was to update Ultrasn0w to work on iOS 4.3.1. iPhone 4 users must take extra care while updating to iOS 4.3.1 as they need to prevent the baseband from upgrading. This update only brings iOS 4.3.1 support to basebands which could be unlocked earlier. Therefore, only baseband 01.59.00 can be unlocked on iPhone 4.

Here's the list of basebands that can be unlocked using Ultrasn0w 1.2.1:

iPhone 4:

  • 01.59.00

iPhone 3G/3GS:

  • 04.26.08
  • 05.11.07
  • 05.12.01
  • 05.12.04
  • 06.15.00
Note: For T-Mobile users in USA should disable 3G under Settings > General > Network. This is due to an incompatibility with T-Mobile’s 3G. Those in other countries do not need to do this, unless they face a problem.

Step 1: Use PwnageTool or Redsn0w to jailbreak your iPhone.
Note: For iPhone 4 users, must use PwnageTool since Redsn0w does not create custom IPSW which is required to prevent baseband upgrade.

Step 2: Launch Cydia on iPhone and add “” as the new repository URL. You can simply tap “Manage” -> “Sources” -> “Edit” -> “Add” to add the repository URL. If your not clear about this, checkout my post here on how to add sources to Cydia. This step only for beginner users, for those who already know about adding repo you may ignore this step.

Step 3: Then tap “Search” and search for “ultrasn0w” application

Step 4 : Install “ultrasn0w” and then on confirm. If you have already installed Ultrasn0w before, you will see a modify button instead of Install, like in the screen shot above.

Step 5: After, Cydia has installed Ultrasn0w, you should reboot your iPhone. To restart, press and hold the power button till you see the slide to power off screen. Now slide the button to turn your iPhone off and then turn it back on. You should now have an unlocked iPhone with iOS 4.3.1.