It looks like a bug in iOS 5 allows you to unlock iPhone 4S without the need to jailbreak it or using hardware methods such as GEVEY SIM.

The bug was discovered by Michael Capozzi. He managed to unlock his iPhone 4S to use it on T-Mobile USA’s network but according to him the method should also work with any GSM carrier.

He has been kind enough to also give the following step-by-step guide to unlock iPhone 4S using the bug in iOS 5 to work on T-Mobile USA:

Note: You will need to cut the T-Mobile SIM to micro-SIM size for it to fit iPhone 4S’s SIM tray.

1. Insert original carrier AT&T SIM card
2. Dial 611 for AT&T customer service hotline and drop the call
3. Turn on Airplane Mode
4. Take out AT&T SIM card
5. Insert T-Mobile SIM card
6. Make sure WiFi is off ( also tap on ‘Forget this Network” to make sure it doesn’t connect automatically later)
7. Switch off Airplane Mode and iPhone will search for network. This is followed by the Apple splash screen appearing.
8. Activation Required will be displayed on the screen
9. EDGE network will activate automatically – notice the ‘E’ on the top left corner of the screen
10. Wait for about 20-30 seconds and turn off the phone
11. Turn on iPhone and the same Activation Required screen will be displayed
12. When you see one signal bar, tap on Use Cellular Connection
13. Eject SIM card
14. Activation Required screen will be displayed the second time
15. Insert SIM card
16. Unlocked!

You can also checkout the video which shows that it works and suggests that the method could also work with iPhone 4 and iPhone 3GS:

Gizmodo has also confirmed that this method works.

Update 1:

Gizmodo and Lg1, one of our regular readers has also confirmed that it works with AT&T iPhone 4 and iPhone 3GS.

Update 2:

This method appears to be temporary, you can read all the details here.

As always, let us know how it goes.

[@chronic via Pastebin, Gizmodo, Thanks Luis for the tip!]