[NoGravitas]

It's semi-correct? You don't lose your contacts, as they're still stored in your phone's address book. But all of your contacts will have to jump ship at the same time as you, to the same silo. And your old contacts will only still be usable if the new silo also uses phone numbers as userids.

On Matrix/Riot, userids are federated in the same way as emails. So when you change providers, your userid changes, but your contacts' stay the same, and you can still connect with them from your new provider.