Federated Chat and VoIP

Has anyone experience to chat or even make VoIP calls between servers (with different domains)?

Nextcloud Talk has an issue on that Federated conversations · Issue #21 · nextcloud/spreed · GitHub

I heard also about matterbridge for Rocket.Chat. And there are some bridges for Matrix.org. Would nextcloud talk or rocket.chat offer this already on Syncloud or would matrix be needed?

As there are also some bridges to Telegram, Signal, and Whatsapp…