AT&T has just started rolling out the Android 4.0 Ice Cream Sandwich update for its variant of the Galaxy S II. The update is available via Samsung’s KIES software, but if for some reason the update is still not available for you and you want to update manually, follow the steps mentioned below.
P.S. – Please make a backup of your data before proceeding with the steps below. Also make sure your phone has sufficient battery left for the flashing process.
Step 1: Download the official Ice Cream Sandwich for AT&T Galaxy S II from here, and ODIN from here. Also make sure that you have SAmsung KIES installed since it will take care of all the required drivers.
Step 2: Extract the firmware file inside a new folder on your desktop. Also fire up ODIN and restart your phone in Download mode. Switch off the phone, re-insert the battery and then press the Volume Up and Volume Down button simultaneously to boot the phone into Download. If you get any warning about custom OS, skip it by using the Volume up button.
Step 3: Connect your phone to the PC now, and ODIN should detect it. When ODIN detects the phone, it will display a random COM No. inside a glowing yellow rectangle. Now, click on the PDA button and select the firmware file that you downloaded in Step 1 and extracted inside a new folder on your desktop.
Step 4: Press the Start button and wait for ODIN to flash the firmware on your phone. When the firmware is flashed, your phone will automatically reboot. Keep in mind that the first boot will take some time so please be patient.
Bingo! You are done! Now enjoy TouchWIZ filled Ice Cream Sandwich on your AT&T Galaxy S2.