ok now mine is restarting with .266 software. I also have a co-worker who is having the issue too with a brand new phone from ATT with .266.
The back casing seems somewhat loose so maybe the battery is disconnecting for a split second. I think I'll try to stick a double sided piece of tape on the casing to make it more snug. You would think they would put a small pad inside the case to keep this from happening.