These are instructions on how to unlock the iPhone 3G for use with any GSM cellphone carrier using UltraSn0w.

Before you can follow these instructions you must have a jailbroken iPhone and you must be on the 04.26.08 baseband(modem firmware). This means that you must be running the 3.0 firmware and have used PwnageTool or RedSn0w to jailbreak.

To find your firmware and modem firmware(baseband) versions you can follow this tutorial. If you are not on baseband version 04.26.08 then you need to follow these tutorials before unlocking: Windows (http://www.symbianize.com/showthread.php?t=126478)

If you are on T-Mobile remember to turn off 3G before starting...

Step One
Press to launch Cydia Installer from your SpringBoard.
http://www.iclarified.com/images/tutorials/4253/16522/16522.png

Step Two
Press to select the Manage tab at the bottom of the screen.
http://www.iclarified.com/images/tutorials/4253/16523/16523.png

Step Three
Press to select the large Sources button
http://www.iclarified.com/images/tutorials/4253/16524/16524.png

Step Four
Press the Edit button at the top right of the screen.
http://www.iclarified.com/images/tutorials/4253/16525/16525.png

Step Five
Press the Add button at the top left of the screen.
http://www.iclarified.com/images/tutorials/4253/16526/16526.png

Step Six
Enter http://repo666.ultrasn0w.com/ as the source url and press the Add Source button.
http://www.iclarified.com/images/tutorials/4253/16527/16527.png

Step Seven
Once the source has been added press the large Return to Cydia button.
http://www.iclarified.com/images/tutorials/4253/16528/16528.png

Step Eight
Press the Done button at the top right of the screen.
http://www.iclarified.com/images/tutorials/4253/16529/16529.png

Step Nine
Press to select repo666.ultrasn0w.com from the list of user entered sources.
http://www.iclarified.com/images/tutorials/4253/16530/16530.png

Step Ten
Press to select ultrasn0w from the list of packages
http://www.iclarified.com/images/tutorials/4253/16531/16531.png

Step Eleven
Press the Install button at the top right of the screen.
http://www.iclarified.com/images/tutorials/4253/16532/16532.png

Step Twelve
Press the Confirm button at the top right of the screen.
http://www.iclarified.com/images/tutorials/4253/16533/16533.png

Step Thirteen
After installation completes successfully press the large Return to Cydia button.
http://www.iclarified.com/images/tutorials/4253/16534/16534.png

Step Fourteen
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.
http://www.iclarified.com/images/tutorials/4253/16539/16539.png

Step Fifteen
You should now be able to insert the SIM of your choice!
http://www.iclarified.com/images/tutorials/4253/16537/16537.pnghttp://www.iclarified.com/images/tutorials/4253/16538/16538.png

***THANKS: A big thank you to all the members of the iPhone Dev-Team for all their hard work! It is much appreciated by all.

***And to iclarified for the instruction.