Just a quick update about iMessage - mine stopped working all of a sudden. I got an error saying to contact apple with a verification reference.
According to a pretty detailed guide on another site there are further verification checks being carried out and if you use many serials / uuids it will block your account.
Anyhow, called apple and they unblocked it but if you get that message then its not about your system, its your account. The other messages around activation still appear to be system led rather than account.
Hope that helps someone.