The link Apple gives is this:
apple.co/IMFT.mac
which goes directly to the Apple maintenance site. I've used it more than once to solve the problem but it didn't help. They use flimsy excuses such as the number was used for spam, therefore the number was blocked, and they say it should be back to normal within 24 hours etc.
It is obvious that there is a real problem with the iMessage and FaceTime service. Every day I am greeted with a bunch of messages on my phone and Mac saying that "a device has been added to iMessage" but nothing improves.
Typical of Apple for not admitting that there is a problem, yet I bet that they are scrambling in the back to correct it.