Well it happened to me a lot lately. Pulling off the the battery does not help at all. it's not app related and does it just about anytime, sometimes while i text, others while playing games, even on iddle on my desk it just reboots. Many times it reboots twice in a row. I though it was heat related (it sometimes overheats @ 46 celcius). I've read it's somehow the OS errors (like a blue screen on windows) that does that.