Today I decided to add my Apple ID to facetime and imessage on my iphone 5. Previously I've only used the phone number for Facetime/iMessage on iphones, and the iCloud ID on the iPad 4 and mini (all running iOS 6.0.1).
When I finished adding the ID to my phone, my iPad asked me if i wanted to use my phone number on my AT&T ipad for iMessage and Facetime, since it was now associated with my apple ID. I said yes, and it KILLED the iMessage and Facetime activation on my iPhone, and reset all my password data on the phone. The iPads were still working fine, but the phone number didn't stick (disapeared at some point).
Rebooting iPhone, removing SIM card, and toggling iMessage and Facetime on and off didn't help to activate iMeesage or Facetime. AT&T replaced the iPhone SIM card, no help. Apple support had me go to Settings > General > Reset > Erase all content and settings, and then restore it from my iCloud backup from 1:12AM today.
The restore of data worked, but it asked me to connect to iTunes to finish syncing my apps and content. A similar thing happened when I restored and iCloud backup to my new iPad mini (had to finish connected to iTunes). I back up to iCloud daily, and to the computer every weekend, so if I'd restored with iTunes I would have lost 3 days of texts and phone long instead of just 1. Afterwards everything was fine and activated.
Then I tried adding my Apple ID to iMessage and Facetime again, and let it try to add the phone number to my iPads again, and this time everything went as planned! If not, I was prepared to wipe and restore again, but give up adding phone number to iPads. I DID NOT need to re-install iOS 6.0.1 from iTunes.
Now I can send and receive iMessages on my iPhone or iPads, and have a copy of the entire conversation showing on all my mobile devices.