Thanks! Right now calls are between Normals accounts only. There's no standard for calls in ActivityPub yet, it covers posts, follows and replies, not real-time audio or video, at least not yet. So there's nothing we could federate a call over yet :(, and as far as I know Mastodon, Lemmy and the rest don't have calls either.
Federated calling does exist on other networks (Matrix, and XMPP with Jingle), but not in the ActivityPub Fediverse. If a standard shows up, we'd love to look at it, as long as calls stay e2e encrypted.