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The iPhone Dev-Team has released the updated version of carrier unlocking tool called Ultrasn0w which can unlock the latest iOS 4.2.1 and 4.1 firmware on iPhone 3GS and 3G on basebands later than 05.13.04. Since iPhone 4 has different baseband OS, It’ll take a little while longer for the Dev Team to unlock it on the latest firmware.

Follow the instructions posted below to unlock your iPhone 3GS or 3G on iOS 4.2.1.

How to: Update iPhone 3GS & 3G to 06.15.00 Baseband for Unlock:
Step 1:
Ultrasn0w 1.2 unlocking requires that your phone is jailbroken on 4.1 or 4.2.1 firmware with 06.15.00 baseband. Follow the complete guide posted here (with PwnageTool) or here (for Redsn0w) to update your iPhone 3GS or 3G baseband to 06.15.00 and jailbreak it on iOS 4.1 / 4.2.1.

How to: Unlock iPhone 3GS & 3G on iOS 4.2.1 / 4.1:
Step 2:
Once you are done with the jailbreak, you can now unlock your iPhone on any baseband using Ultrasn0w 1.2 from Cydia. To do this:

  • Run the “Cydia” app on your iPhone.
  • Tap on the “Manage” tab at the bottom.
  • Tap “Sources”. See the screenshot below:

4.2.1 Unlock

  • Now Tap on “Edit” and then tap on “Add”. A message-box like popup will appear asking you to enter a Source URL (See the screenshot below). Type http://repo666.ultrasn0w.comand tap on“Add Source”.

4.2.1 Unlock (1)

Cydia will perform an update of sources by downloading files from the repository.

  • When Cydia is done with the installation, Search for “ultrasn0w 1.2” and install this application. Installing this app will automatically unlock your iPhone and you will be able to use your iPhone with any carrier.

Ultrasn0w 1.2

Step 3: Restart your iPhone and it will boot to an unlocked state. You can use your iPhone 3GS or 3G running iOS 4.2.1 with any carrier !

Video instructions for the above tutorial is embedded below:

Disclaimer: This guide is for testing & educational purposes only. I’m not responsible for any loss of important data or malfunctioning of your iPhone.

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