@devrtz I managed to connect linphone.org, but it doesn't work. Can't call another client. I guess linphone and gnome calls app isn't fully compatible. So far @fluxer.app most promising VoIP for me. Or I should start self host server

quick update to this thread (sept 2018). Linphone app is getting really, really good and is already working for SIP I've tested with my business SIP phone and it's now 'working' . There is a telegram group and also a kind of active community around this app if anyone is interested you can PM me or if @CiberSheep wants to open the group up in this thread he can....