I've had the iPhone 4S since launch but during the past week it has shut down 3 times just by itself. All 3 times the only way I can get it to boot again is by holding down the power and home button. The power button does nothing at all and plugging it into a power outlet or my mba does nothing. Every time it boots back up it shows that the battery is not empty or even in red, so that's definitely not the issue. Has anyone else experienced something like this?