xoicos from Twitter discovered a way to unlock your iPhone4S without the need of a jailbreak. Please do this at your own risk. I have tested it and can confirm that it is working(although it took me a few tries to get the timing right). Insert original carrier AT&T SIM card Dial 611 for AT&T customer service hotline and drop the call Turn on Airplane Mode Take out AT&T SIM card Insert T-Mobile SIM card Make sure WiFi is off ( also tap on ‘Forget this Network” to make sure it doesn’t connect automatically later) Switch off Airplane Mode and iPhone will search for network. This is followed by the Apple splash screen appearing. Activation Required will be displayed on the screen EDGE network will activate automatically – notice the ‘E’ on the top left corner of the screen Wait for about 20-30 seconds and turn off the phone Turn on iPhone and the same Activation Required screen will be displayed When you see one signal bar, tap on Use Cellular Connection Eject SIM card Activation Required screen will be displayed the second time Insert SIM card Your Iphone 4S Unlocked!