Own_server (migrate)

If you create a username it is stored on ns.jami.net.

Link: https://git.jami.net/savoirfairelinux/jami-project/-/wikis/tutorials/Frequently-Asked-Questions#account-8

By default, a username is registered on ns.jami.net where you can’t modify the Jami ID associated to this username. So, if you delete or if you lost your account you will not be able to retrieve this username, ever. Nobody will be able to recreate an account with the same username.

Actually you can have 5 (different) servers:

[…] but while servers are not required, they are still used in five specific cases: push notifications, the OpenDHT proxy, bootstrap, name server, and TURN

AND:

The bootstrap, TURN, and name servers can all be configured in the advanced Jami parameters and users can use their own if they wish.