On Thursday AT&T released the Android 4.0 Ice Cream Sandwich update for their Samsung Galaxy S II. Out of the two version, the update is released only for the original Galaxy S II and is not available for Skyrocket version of the phone.
The update was not released over-the-air and is only available via Samsung Kies. Connect your Galaxy S II to a PC and use Samsung Kies to get the update.
The leaked Ice Cream Sandwich update was made available more than two months ago for AT&T’s original Galaxy S II. The update for Galaxy S II Skyrocket was also leaked around the same time and was tested to be working without any issues on AT&T handsets.
SOURCE: Android Community