Sony is now rolling out the Android 4.0 Ice Cream Sandwich update for the Sony Xperia ion for AT&T. You can download the update using the Sony PC Companion software. The device will receive Android 4.0.4 with software version 6.1.c.1.105 on the LT28AT model.If you have not received the update notification, you can manually check for the update availability through settings. Sony has still not released a change-log for this update, but we will have it up for you as soon as they do.
source – XDA Developers