Imagine a fictional app called Thneed that can track my chats in multiple apps, without implementing any C2S protocols internally.
* When I create a Thneed chat, it opens the address book so I can choose a contact, and if I have more than one for them, choose which address to chat with them on.
* Once I've typed a message in that chat and hit send, Thneed opens the default app on my device for the app associated with that address, and forwards the text of my message to that app
(5/?)