When is a touchscreen not a touchscreen? Increasingly, it's when your smartphone reads your eyes, gestures and movements to perform basic functions without tapping the screen at all. That was Samsung's point Thursday with the rollout of the new Galaxy S IV, the latest from the company's flagship line and the first Android-based phone to seriously challenge Apple's iPhone for dominance in the mobile market. The phone will be available on all major U.S. carriers by the end of April.