iPhone Dev-Team has released new information on the free carrier unlock software package known as ultrasn0w. Now iPhone 3G and iPhone 3GS devices running baseband versions 04.26.08, 05.11.07, 05.12.01, 05.13.04, and 06.15.00 are unlockable after jailbreaking. iPhone Dev-Team includes detailed ultrasn0w information in their recent Ultra-recycle blog post.
Running iOS 4.2.1 on your iPhone 3G/3GS? Updating your iPhone baseband to 06.15.00 using iPad 3.2.2 firmware actually makes the device unlockable for use on carriers other than AT&T Mobility. Dev-Team has developed a PwnageTool 4.1.3 Unlock Edition that will update the 3G/3GS baseband, and the group is working on a new version of redsn0w that will add this functionality for Windows users.
iPhone 3G and 3GS models running basebands higher than 05.13.04 or lower than 06.15.00 are not unlockable with ultrasn0w at this time. Dev-Team made news this week by releasing an iOS 4.2.1 jailbreak immediately after Apple launched the new firmware. The first step in unlocking is to jailbreak, so here are instructions on how to jailbreak your iPhone running iOS 4.2.1.
After jailbreaking and insuring you have a compatible baseband version, Cydia should already have the repository repo666.ultrasn0w.com pre-installed. From here, you can download and install ultrasn0w. T-Mobile is currently the only iPhone-compatible carrier in the US besides AT&T. Most analysts believe an end to the exclusive contract between Apple and AT&T is imminent and could result in unlocked iPhones being sold in the US as they are in other countries.