I first mentioned having this problem ever since the ICS update. I went to the Sprint store and first they said I had a bum battery... They exchanged the battery and it continued to happened. After going back to the store they decided to replace the unit and it continued to happened. I'm on the second replacement phone now and decided that it might not be the phone since three phones (my original and two replacements) can't have the same exact problem and I didn't see many posts mentioning people having problems with their NS4G rebooting after ICS. I decided it has to be one of my apps so i uninstalled everything for about a day or two and guess what? My phone did not reboot....I gradually reinstalled certain apps and it continued to behave with no reboots. Yesterday, I reinstalled green power battery save and wouldn't you know it my phone rebooted itself. So I figured that must be the app that's causing the phone to reboot... I uninstalled reboot last night almost 24hours later no rebooting. by the way, i am running stock.