“ Originally Posted by BiG JeW 
”
WOW... i dunno... never heard of that happening randomly.. unless the phone is in the pocket.. I know that occasionally it may ask you ... Are you sure you wanna power off the device or go into flightmode? Then you have the option of selecting yes or no.. If you dont selcect a option, it has a tendency to turn off. It shouldnt turn off in the middle of using it unless you clicked something. I would try a hard reset in your case!
i have to agree with jew and if after a hard reset it is still doing it bring it into sprint and tell them whats going on..... they will give you a new one for sure.