My friend wants me to unlock his 3GS, but I'm running into mixed problems with this. i read the serial number is what tells if you can unlock the phone or not, but I was also told it'd the firmware. It's on 5.16.05, which I'm reading can't be unlocked unless you trace back to 4.2.1 and set the phone up as if it were on that firmware. Is there no other method to have an unlocked firmware of 5. anything? Really need some help here guys, so if anyone can speak out it'd be greatly appreciated.