How do I change my MacBook FaceTime cell phone number? I have a new cell phone number, and, as my FaceTime on my MacBook still has the old number, and so does my iMessage, I'd like to change it. How can I do it?

Apparently, the only option given, under FaceTime's preferences, is to add another email
You can change the phone number associated with your appleid on http://appleid.apple.com 

I know that when you update mail addresses there they also update your facetime account, I suppose it should be the same for telephone numbers.