Apple says that some users may be experiencing iMessage and Facetime issues
thenextweb.com
thenextweb.com
edit: clarified
I like the ability to contact phone numbers rather than user IDs, but apart from that, one AIM account on all devices seems to be a better proposition, at least in my experience.
And for the record, yes, I still use AIM.
This is using T-Mobile in the Netherlands.