When upgrading my macbook pro (third mtn lion upgrade) received an error on imessage setup that I could not use my Apple ID at this time. Called support and since my pro was past 90 days thought I would have to pay for the issue. Asked for supervisor. As it turns out I guess you have to call now to activate imessage if you have multiple machines!
Very unApple like. I guess it doesn't "just work". Come on Apple at lease make the message a bit more clear or provide some way of self verification.