Signal, Telegram, Wire, Jitsi and Linphone. The first three of these are relatively well known and used, seemingly unlike Jitsi and Linphone.
The people of Linphone offer a SIP address to use for their software. The SIP provider is what provides the strength of the call quality. Using Linphone with their SIP address, I was experiencing call drops at higher frequencies than competitor software. I wasn’t able to find a better SIP provider to give Linphone better call quality. Messages also often failed to be sent on the Android client, though I wonder if that was due to battery optimisation that may or may not have been on.
I’ve tried Jitsi using the Linphone’s SIP. Pretty decent client. I’ve tried extensively trying to work out how to use Jitsi without using Linphone’s SIP, because it seems on the poorer side, but I’ve had no luck. I’ve seriously spent hours on it using search engines trying to work it out and all I’ve accomplished by doing so is to feel like an idiot. More recently, Jitsi has released software called “JitsiMeet”, which is a pure video conferencing client that doesn’t require setting up an SIP or any of that. Seems to work decently.