Two tings generally cause a spontaneous reboot of an IP phone: momentary loss of power, or network disconnects lasting longer than 60 seconds. Your network may be solid, but patch cords can break, jacks can go bad. While it may not be your network per se causing this, it's almost surely network related.

Sometimes the thoughts in my head get so bored, they go for a stroll through my mouth. This is rarely a good thing.