I don't know if any of you are utilizing the AT&T Voicemail Viewer app (for listening to your home/office voicemails), but I was experiencing similar issues with frequent reboots. It was very odd - I could even be on a call, the call would apparently end and I couldn't do anything on the device. After a minute or so, it would appear to reboot and once it came back up, the call would begin again (it never dropped the call even with the reboot!). I traded in my device on warranty and got another - same thing started happening. So I restored the device and started installing apps 1 by 1 each day. everything was working fine until I installed the Voicemail Viewer app and set it up. Almost immediately I started experiencing the same problem, especially when I went in and out of WIFI connections. I looked at the comments in Google Play for this app and found lots of issues specific to Galaxy Note 2 and the S3. Here's some examples:
"My GS3 has been driving me crazy resetting whenever I turn WiFi off of am out of range of WiFi. It took me a LONG time to isolate the problem to THIS app. When this app works it is very handy to get our home voice messages delivered direct to the phone, this app breaking the phone is not a good tradeoff."
"After updating to Samsung / AT&T stock JB 4.1.1 ROM this app causes my phone to freeze or lockup all the time. The phone (or maybe just TouchWiz) always freezes when leaving a WiFi network or when disabling WiFi. As soon as a voice mailbox is configured this starts happening. Took me two months to find out it was this app since I have 100+ installed!"
"I sent an email to the developer about this and have written about this on android central forums. My Galaxy Note 2 would hang up then reboot after leaving a wifi network (or if you turned wifi off). After five weeks of diligently noting all the changes I made to the phone and testing out each change (starting from booting in safe mode to uninstalling different apps, etc.), not to mention exchanging my original Note2 for another one and doing a master reset twice, I narrowed my problems down to this app. After completely uninstalling it, I have not had a hang/reboot of my note 2 when leaving a wifi area and going into cell data (or if I turned wifi off manually). You may not even notice you have this problem because the reboot happens quietly (if it's asking for your pin again and again, it's probably because your phone rebooted). If you have this app and a note 2, do this simple test: go to a wifi area like your home network, start this app, look at the voicemail listing, and turn off wifi. If your Note 2 does not hang up then reboot in a few seconds, you're good. If it hangs up and reboots, then completely uninstall this program"
Hopefully maybe this provides a solution for some of you experiencing this. Since I uninstalled the app, I've not have a single reboot.