Believe it or not: #deltachat is growing audio/video calls starting with the currently rolling 2.22 releases ... A few people already had two hour long stable calls :)
Calls are an experimental option while we continue to work on reliability, UX/UI revisions, and configuration of TURN servers on #chatmail relays and in clients.
We want calls to reliably work across all major platforms, networks and phones, including #UbuntuTouch
Feedback and debugging happens at https://support.delta.chat/t/help-testing-upcoming-delta-chat-release-with-calls/4220/17