I noticed a major bug that causes the phone to reboot randomly, freeze and require a hard restart, reboot upon making or answering a phone call. I am running iOS6 Beta 2 on a 4S 32GB on AT&T. This problem started just a few days ago and NEVER happened prior to the first incident. It started out completely random and never could reproduce until yesterday and today.
I realized that the timeframe for when the problem began lined up with when I downloaded and installed the latest Twitter update. I believe the new version is 4.3 coming from 4.2. So if you are running iOS6 Beta on your device and have yet to update the official Twitter app, DON'T!
The other reason I think it is related to Twitter is yesterday when it rebooted it gave me a Notification window (just like the old SMS text notification pre-iOS5) asking for twitter access to contacts and in the message there was a random "(null)" mid message for no apparent reason. I had to options "Allow" and "Deny" and neither of them did anything when I tapped on them. I had to do a hard restart in order to get the message to disappear and to use the phone.
I have since deleted the official Twitter app this morning and have yet to experience the glitch again. Hoping that it does not happen again. I may try re-installing the Twitter app later to see if a fresh install will work. If the bug goes away and doesn't happen again after the fresh install I will post back my results. Until then I recommend not updating the official Twitter app.