Dev-team has released the v1.2 of ultrasn0w that unlocks iOS 4.2.1 on iPhone 3G and iPhone 3GS with baseband 04.26.08, 05.11.07, 05.12.01, 05.13.04 and 06.15.00. iPhone 4 is not supported as it has different baseband.

Following are the complete guide and details to unlock iOS 4.2.1 on iPhone 3G and 3GS using ultrasn0w.

Important things to know before you go for this unlock:

  1. The unlock is for iPhone 3G and iPhone 3GS with baseband 04.26.08, 05.11.07, 05.12.01, 05.13.04 and 06.15.00.
  2. iOS 4.1 on baseband 05.14.02 and iOS 4.2.1 on baseband 05.15.04 are NOT SUPPORTED.
  3. YOU CAN UPDATE YOUR BASEBAND to 6.15.00. Read this guide from RedmondPie for full details.
  4. If you update to baseband 6.15.00, you won’t be able to downgrade the baseband.
  5. It is HIGHLY RECOMMENDED that you should not upgrade your baseband to 6.15.00. Only do this if you are in need of unlock after updating to iOS 4.2.1 or you are suck with baseband 05.14 or 05.15.

How to unlock:

  1. Jailbreak your iPhone running iOS 4.2.1 with Redsn0w by following guide here.
  2. Run Cydia on your jailbroken iPhone 4.
  3. Tap ‘manage’ at the bottom of the screen and then ‘click Sources’IMG_0204
  4. Tap the ‘edit’ button at the top right of the screen and then tap ‘Add’ button on the top left of screen.
  5. Enter http://repo666.ultrasn0w.com as the source of URL and tap ‘Add Source’ button.IMG_0205
  6. When your done with adding source, tap ‘Return to Cydia’ button and press the ‘Done’ button at the top right of the screen.
  7. Select http://repo666.ultrasn0w.com/ from the list of user entered sources and select ultrasn0w from the list of Packages.
  8. Tap ‘Install’ button at the top right of screen and then tap ‘Confirm’ to start the installation.
  9. When installations completes successfully, restart your iPhone.
  10. After reboot, hold the ‘home’ button and power off the iPhone and then turn it on again while you hold the ‘home’ button.
  11. Done, you can now enjoy your unlocked iPhone running iOS 4.2.1.