I use JMP.chat and Gajim. Works pretty well. I call people they call me. I updated to the recommended PAVUControl settings. I haven’t had as many complaints about the echo.
It is not perfect. Sometimes calls are dropped. Sometimes the modem shuts down. It is still buggy but I accept that. It seems like a fair number of things on the Librem 5 are just a tad buggy. Again, I accept this. Purism and the developers seem to be making consistent changes and I am very pleased with the updates.
It isn’t perfect but it does the job for me. I can call people on wifi and text them from a number that costs me about $1.50 a month. I’ll take it.