The method has been reported to work on the iPhone 4 and the iPhone 3GS as well.
NOTE - You will have to convert your mini SIM to a micro SIM for the iPhone 4 or iPhone 4S, you can always get a microSIM from your carrier if they have it available. You can read our guide on how to convert a mini SIM to micro SIM here.
NOTE - MuscleNerd from the Dev-Team has confirmed that this method will be temporary on carriers who perform a TMSI.
it’ll just relock again once a new TMSI is required (various normal network operations require TMSI refresh). If you are successful at temporarily gaining network access, you’ll lose it as soon as TMSI is refreshed (happens often). the TMSI refresh is a normal, regular action on the network (it’s actually intended to protect you).So keeping in mind that this method may not be a permanent solution, Check out the guide to unlock your iPhone without the need for hardware (GEVEY SIM) or software (UltraSn0w) modifications
- Insert original AT&T SIM card
- Dial 611 for AT&T customer support and immediately drop the call
- Turn on Airplane mode
- Remove the AT&T SIM card
- Insert T-Mobile (or your own carrier) SIM card
- Make sure Wi-Fi is switched off. Clear existing connections so your phone doesnt connect automatically.
- Switch off Airplane mode and allow the phone to search for a network.
- Activation Required will be displayed on the screen
- EDGE Network will activate automatically. You can see the 'E' displayed o the top left corner of the screen
- Wait for 20-30 seconds and turn off the phone.
- Turn your device back on and the activation required will be displayed again.
- When you see one signal bar, select Use Cellular Connection
- Eject SIM card
- Activation required will be displayed one last time
- Insert SIM card
- That's it, your device should now be unlocked.
Here is a video of thus method in action