Unlocking the iPhone has always required jailbreaking and paying close attention to custom firmware and basebands. Now thanks to a simple process, the iPhone 4S can be unlocked without jailbreaking. This process makes use of a bug in iOS 5 and allows the iPhone to be used on T-Mobile. Of course, there are some caveats.
As OS X Daily reports, some users have had to go through the process several times to make it work. This process requires an AT&T (GSM) iPhone 4S, and will not work with the Verizon or Sprint iPhone. Also, the T-Mobile SIM card must be cut down to Micro SIM size before the process begins in order to fit in the iPhone 4S.
The unlock described here is a temporary unlock, meaning it will work until the Temporary Mobile Subscriber Identity (TMSI) is changed by the carrier. Although this can be changed at any time for security, it will usually be changed when the iPhone enters a different geographic area on the carrier's network. If the TMSI changes the iPhone 4S becomes unlocked and you'll have to repeat the process.
Once you have your T-Mobile SIM cut down to size and an AT&T iPhone 4S you're ready to unlock without jailbreaking. Here are the instructions on how to unlock the iPhone 4S:1. Make sure your original AT&T SIM card is installed and dial 611 for service
2. Drop the call then turn on Airplane Mode (Settings -> Airplane Mode -> ON)
3. Swap out the AT&T SIM card and install the T-Mobile SIM card
4. Make sure Wi-Fi is off (Settings -> Wi-Fi -> OFF)
5. Now turn off Airplane Mode and the iPhone 4S will search for a cellular network
6. You will see Activation Required on the screen
7. EDGE will activate automatically, wait 20-30 seconds for next step
8. Reboot the iPhone and Activation Required will appear again
9. When you see a signal bar select Use Cellular Connection then remove SIM
10. Activation Required screen will appear again, insert SIM and iPhone is unlocked
Apple currently sells unlocked iPhone 4S models, however because there's no carrier subsidy for entering into a service contract, buyers will have to pay full price. This amounts to an extra $450, putting the unlocked iPhone 4S 16GB model at $649.