I unlocked my iPhone so that I could go overseas and use a local number. Im not trying to cheat Apple out of their 5 bucks a month that they get from my AT&T account.
I unlocked with iUnlock.app which is the precursor to AnySim. I had my iPhone stuck on 1.0.2 due to bricking concerns.
After seeing the update at Macworld, I couldn't resist and successfully virginized my iPhone's baseband firmware so that I could safetly upgrade my iPhone to the latest firmware.
I used this method:
Unlock the iPhone - the simple tutorial!
It was really quick and painless. It's a script that runs through Installer.app. There's no need to use the terminal or anything. I just thought I'd chime in here and say that it worked perfectly on my iPhone so if anyone here with an unlocked iPhone and an AT&T account wants to update their firmware, head on over to the above link.