Finally the new version of Ultrasn0w is released to Unlock the iPhone 4, iPhone 3GS, and iPhone 3G. Before you can follow these instructions you must have a jailbroken iPhone and you must be on the 04.26.08, 05.11.07, 05.12.01, 05.13.04, or 01.59 baseband(modem firmware).
Here are the Instruction to unlock your iPhone 4
1. Jailbreak your iPhone using JailbreakMe.
2. Press to launch Cydia Installer from your SpringBoard.
3. Press to select the Manage tab at the bottom of the screen.
4. Press to select the large Sources button
5. Press the Add button at the top left of the screen.
6. Enter http://repo666.ultrasn0w.com/ as the source url and press the Add Source button.
7. Once the source has been added press the large Return to Cydia button.
8. Press the Done button.
9. Press to select repo666.ultrasn0w.com from the list of user entered sources.
10. Press the Install button at the top right of the screen.
11. Press the Confirm button at the top right of the screen.
12. After installation completes successfully press the large Return to Cydia button.
13. Reboot your iPhone.
You should now be able to insert the SIM of your choice!