I'm using a Cingular (GSM) Treo 650. I was getting lots of resets on my Treo. I could consistently duplicate the problem by using my stylus to access the options menu of from the dialpad. I finally traced the problem to the program "Fields Plus." After I deleted "Fields Plus" the resets disapeared!
What a pain! I had to delete the programs one by one until I couldn't force a reset. AAAAAAAAAAAAAGGGGGGHHH!