Sorry to report that the log files were a dead end -- not showing us what we needed to know. (Thanks so much to those of you who helped us by sending them!) I will be reaching out to a few of you to get some of these devices back for investigation.
Well, we tried. But it looks now like understanding the reasons this small number of phones experience regular reboots is going to take some time and investigation. If your rebooting problem is serious, at this time I think you should consider taking it back to your place of purchase for an exchange. It's your call -- mine rebooted the other day, and it did it a couple of times in the first week that I started using it. For me, that's not a big deal. My PC crashes sometimes too. But if you can't rely on the phone, that's different.
Again, thanks for the help and patience!