unlock fusion worked for me today
Bought it yesterday evening after reading this thread, and got the code about 12 hours later. Worked perfectly on my iPhone 4 (ATT). Only $13.45!
And to clairfy the process for anyone, this is how I did it:
1. Connect iphone to itunes and perform a backup (right-click on iPhone name in left panel, then choose backup)
2. In my case, I removed my previously installed Gevey SIM, then rebooted the phone and connected to iTunes.
3. Perform a "Restore" by clicking the Restore button on the main iTunes screen. This updated me from iOS 4.3.3 to iOS 5.1.1, and took a litttle while to complete. I was a little worried here as I knew it would update my Gevey unlockable baseband.
4. After the restore was finally finished, itunes said "Congratulations your iPhone is now unlocked." Yay!
5. I then did a restore from backup to put my contacts and everything back onto the phone. Working great on T-mobile.