If, now, you move your voice to a social app, what happens to your phone number? Do you still use it in the WhatsApp sense, as an ID number rather like an ICQ ID? Does it still matter if it changes? Or does it linger on as something for old people and as a mailbox for boring official things (like email?).
Next, do we think differently about fragmentation of voice than of messaging? It seems clear that we are not going to have one single point of contact for messaging systems. Everyone will have several of Facebook, LinkedIn, WhatsApp, Line and so on, with new apps coming and going, some quickly like fireworks, some finding a way to stick. But are we happy having multiple paths for voice in the same way? I can’t think of an a priori reason why it would be different, other than perhaps urgency, but who knows?
This is the future I am simultaneously praying for and dreading. Leaving phone numbers for superior forms of identity will be great; having to maintain a presence across n number of services will not be.