I wrote a basic softphone for #nostr (it uses nostr relays for #webrtc signaling) called #voistr: https://voistr.codeberg.page/

More features are planned, chat and maybe video calls. Both the signaling exchange and the voistr protocol use NIP-44 encrypted events. Follow voistr here: nostr:npub1lcfnjgme4s9whl6n4fym0ft034rdmghahal7jzg7zw35w8f6dq2s2kn6vm