Looks like someone has discovered a way to unlock your iPhone without having to make any modifications to the hardware or software (via 9to5Mac).However, it’s reported that this will only work until the TMSI is refreshed, so it probably won’t last long.
According to the directions, this works on the iPhone 3GS, iPhone 4 and iPhone 4S, and you will have to redo the process if you reset the device.
Here’s how it works, know that we have not tested this out for ourselves. Use it at your own risk:
1) Cut your T-Mobile SIM to match the AT&T SIM.
2) Put your AT&T SIM in the iPhone.
3) Dial 611 for AT&T customer service and drop the call
4) Turn on Airplane mode
5) Remove the AT&T SIM
6) Pop in the T-Mobile SIM
7) Turn off wifi and tap ‘Forget this Network’ this is to ensure that it doesn’t auto connect to your network later.
8) Turn Airplane mode off and your device will search for a network. The Apple splash screen should now pop up.
9) The screen will say “Activation Required”
10) The Edge network will now activate automatically
11) Wait 20 or 30 seconds and turn off your iPhone.
12) Turn your iPhone back on and you will see the Activation Required screen again. When one signal bar comes up, tap on “Use Cellular Connection”
13) Eject your SIM
14) You will see the Activation Required screen again
15) Pop the SIM back in and you should be unlocked.