My phone has done this twice once just in my pocket and the second time I was on the phone talking to someone. I had to call Verizon support for a App that I installed that wouldn't work on the Droid X and he helped me uninstall it and I also asked him about the restart problem I had and he adviced me to turn the phone off for a period of time every day because it is just like a small computer and see if that helps. I am not sure if it has helped or not because it hasn't done it again so maybe it does help if you do turn it off.