One model that could work I thought of works like this: A packet based P2P network, where peers can also act as buffers to relay the packets. So basically the

One model that could work I thought of works like this: A packet based P2P network, where peers can also act as buffers to relay the packets. So basically the same as servers in the traditional sever client model. However your account isn't bound to a server like with email or diaspora. So the networks of computers of your friends can act as servers serving your smartphone. Or the developer of the app you use can provide a server that can also send you push notifications. The real problem for decentral messaging/social networks is discovering your friends. Friends of friends being suggested to you certainly is a good step forward but it's not enough. It doesn't work when creating a new account and when adding people outside of your friend's circle.