This is not a rooted rom. This is the official release! I just upgraded my T-Mobile Galaxy S2′s Android firmware from Gingerbread (2.3.6) to Ice Cream Sandwich (4.0.3) and recorded the whole process. I didn’t encounter any major problems, and so far the ICS update is working perfectly Proceed at your own risk though. I had no problems, but that doesn’t mean for sure that you won’t. TIPS & NOTES: Make sure you **backup everything on your phone** before performing the upgrade. Make sure your battery is fairly full. You must also already have Gingerbread (Android 2.3.6) in order to upgrade to ICS 4.0.3 ! If you have any connection problems with Kies, restart your PC and your phone, and try again. Kies can also be fairly slow, so give it a little time before you conclude it’s not working. DO NOT UNPLUG your phone while the update is running. Set it down, and don’t touch it until the update is complete. I would also recommend not plugging your phone into a USB hub while performing the update. Use one of the main USB 2.0 ports on your PC. Make sure your computer is not set to sleep or shutdown while idle. If you cannot live without your phone for a few days, do not try this, and just wait for the OTA update! I’ve read that some people have had issues and bricked their phones. You would then have to take it into a T-Mobile store for a fix. I have a backup phone, so I was willing to take the risk. I probably won’t have time to help you out if you have problems, so read the …
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Updating T-Mobile’s Samsung Galaxy S2 to Ice Cream Sandwich (Android 4.0.3 ICS) Official Release