Jitsi. https://jitsi.org/ https://jitsi.org/ FOSS, cross-platform (not mobile yet though, if you can throw money at that, it can be done), encrypted audio/vide

Jitsi. https://jitsi.org/ https://jitsi.org/ FOSS, cross-platform (not mobile yet though, if you can throw money at that, it can be done), encrypted audio/video, in active development. You can use any XMPP account you like. It even has call recording built in which is very handy if you might need to remember or protocol things.