Signal, Wire, Privus SecurLine, Riot (Matrix), Threema are good candidates for audio and text secure communications.
Some leak metadata, some have countermeasures like not using own's phone number (SecurLine and Threema) or using fixed bitrate for audio calls (Signal, Wire, SecurLine).
If you want privacy and trust choose a solution in that you can audit the source code and that it is verified by a third party auditor.
This is a fascinating and well elaborated article!
I noticed that UX/UI is important and a guarantee that SAS should increase in length, what are some of the recommendations that you advise to have a good ZRTP implementation ?
Or should we start discussing the fadeoff of ZRTP and a change to something like Matrix protocol or even Signal's one ?