you can try reloading the OS again. i was having problems with imessage not activating on ios6 after i was using a prepaid SIM while in Iceland for a week. it worked perfectly while there, but when i put my verizon sim back in, no dice. i had to reload the OS then restore to a previous backup.
are you guys stuck on activation? when i went to beta 2, my imessage was activated properly upon updating, but my phone number was greyed out. i had to hard reboot to allow it to use my number as an imessage address.