UltraSn0w is a small daemon that is launched on boot. It injects the payload at boot and also whenever there is a baseband reset. You won’t notice anything about it other than that your third-party sim now works. Once you have a Jailbreaked iPhone then you can use these easy steps to Unlock your iPhone. Note: This unlocking guide will work for you only if your Modem Firmware (Baseband) version is 04.26.08. If you have upgraded directly to iPhone 3.1.2 stock firmware from iTunes then you are pretty much out of luck for now.

How to Unlock iPhone 3G 3GS 3.1.2 firmware with Ultrasn0w?

  1. Download and install the latest version of iTunes if you haven’t already.

  2. Follow the guide here to jailbreak your iPhone 3G or 3GS using PwnageTool on firmware 3.1.2.

  3. Once you are done with the jailbreak, you can now unlock your iPhone running jailbroken firmware 3.1.2 by using ultrasn0w 0.9.

  4. Press to launch Cydia Installer from your Springboard.

  5. Press to select the Manage tab at the bottom of the screen and touch on Sources

  6. Touch on “Edit” and then on “Add”. You will be prompted to enter a url source as seen in the screenshot below. Type “http://repo666.ultrasn0w.com” and touch on “Add Source”.

  7. Cydia will now automatically update your sources by following a series of automated steps.

  8. After installation is completed. Search for “ultrasn0w” in Cydia and install this application. This app will automatically unlock your iPhone so that you can use it with any carrier.

  9. Now press the Home button then power off and power on the iPhone. You do this by holding down the power button for 3 seconds then moving the power slider that appears to the right. Press the power button again to turn on the phone.

  10. You should now be able to insert the SIM of your choice! Update 1: I can see from the comments most of the people who are saying the tool didn’t work are having baseband 5.11.07. I had clearly mentioned in the article (under Note) that this will work only for users on baseband 04.26.08 Update 2: Good news! Blacksn0w to Unlock 05.11.07 Baseband on iPhone 3.1.2 Firmware Update 3: Unlock iPhone 3.1.2 baseband 05.11.07 With BlackSn0w Thanks RedmondPie!