[haffenloher]

> Switching from Signal to WhatsAPP is very expansive because you need to rebuilt your social [graph]

It's not and you don't, because your entire social graph is on your phone, in your address book. That's precisely the point. As the identifiers and contact lists are owned by the users and not by the messaging service providers, switching between messaging services (taking your social graph with you) is about as easy as it gets. See https://whispersystems.org/blog/contact-discovery/