They do support it (Settings -> Advanced ->enable Debug calls or wait a few days for the latest release). Also chatmail servers provide turn/stun for calls if they couldn't established as p2p.
Yes, p2p or via turn server, always encrypted the same way as messages.
Full topic is here: https://support.delta.chat/...
The latest version also got much nicer calls interface: https://deltachat.github.io/...
thanks for using Leebra!
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