I was using the phone normally, not talking, just messing around and all of a sudden it deactivated.
I went all the way back to the original iPhone Setup screen like it wanted to set it up again. This happened to both mine and my wife's phone around the same time.
I tried:
1. Restoring back to iOS 5 Beta 4 - would not activate
2. Restoring to iOS 5 Beta 2 - would not activate
3. Restoring back to 4.3.3 - would not restore, said ineligible even after entering DFU mode
4. Finally had to restore back to 4.3.5 after entering DFU mode to get it to work and sync properly.
So now my iPhone is back on 4.3.5 and everything is working but I cannot reinstall iOS 5 Beta. I have no idea what happened but it affected mine and my wife's iPhones and now we are both back on 4.3.5.
I have a feeling that the developer that added my UDID to their account either removed our UDID's for some reason or his account was wiped by Apple. Either way, I'm pissed. I couldn't restore from any recent backups because all of my recent backups were from iOS 5 and they would not restore to iOS 4.3.5, I had to restore from a backup that was taken 2 months ago.
My wife couldn't restore her's from backup at all because her computer was recently wiped and reloaded with Lion and all of her backups were taken from iOS 5, she had no previous backups still on her Macbook so she lost a TON of stuff. 
I don't see anyone else having this issue so I don't think it's an Apple activation server issue, it seems that my UDID was removed and thus deactivating my iPhones.
SUCKS!

*end rant*
I tried:
1. Restoring back to iOS 5 Beta 4 - would not activate
2. Restoring to iOS 5 Beta 2 - would not activate
3. Restoring back to 4.3.3 - would not restore, said ineligible even after entering DFU mode
4. Finally had to restore back to 4.3.5 after entering DFU mode to get it to work and sync properly.
So now my iPhone is back on 4.3.5 and everything is working but I cannot reinstall iOS 5 Beta. I have no idea what happened but it affected mine and my wife's iPhones and now we are both back on 4.3.5.
I have a feeling that the developer that added my UDID to their account either removed our UDID's for some reason or his account was wiped by Apple. Either way, I'm pissed. I couldn't restore from any recent backups because all of my recent backups were from iOS 5 and they would not restore to iOS 4.3.5, I had to restore from a backup that was taken 2 months ago.
I don't see anyone else having this issue so I don't think it's an Apple activation server issue, it seems that my UDID was removed and thus deactivating my iPhones.
SUCKS!
*end rant*