This is only a thought.... a friend of mine had reboots because the RAM usage got down so low the only other thing the phone knew to do was to reboot... I have an app call "Fast Reboot" on my phone, this is similar to the Advanced Task killer, but instead of running all the time as a background process, I just tap on the "Fast Reboot " app and it frees up my ram.. I do this daily. and just to check on the settings and aboutphone, and battery.. it still keeps my uptime from the last time i did a full restart.. so the fast reboot does not clear out that setting.. don't know if it helps but it could be a way to see if it's low ram.. or if it's an issue with the phone.