Ice Cream Sandwich features upgraded functionality and new features, such as Face Unlock. By looking directly at the screen, the smartphone recognizes its owner and automatically unlocks the device.
The upgrade also includes speech-to-text technology and the ability to dismiss individual notifications by swiping a finger over the item even while the phone is locked. For easy multitasking, switch between apps using the Recent Apps feature and even close unused ones by just swiping them with a finger.
Additional information on the Ice Cream Sandwich upgrade can be found on the HTC Rezound support page.