Can you rattle off your facebook account number? Chances are, few people are more than semi-consciously aware that such a thing exists.

Chances are the phone number will remain, but it won't be important ... like Facebook, and like modern phones, you deliberately connect with someone. True with modern phones you do consciously give them a number whereas with Facebook you don't (even though it's the underlying account id #'s used by Facebook's infrastructure), but there are other options such as bumping someone's phone with yours to initiate transfer of some piece of data or other.

I would like to think it'll soon be slowly replaced by something more sophisticated.

Personally, I'd love to have control over who can contact me and by what means - basically, grant access to specific pieces of my contact information to specific third parties where I can revoke access at any time and they get any updates I make instantly.