I am good at voip,asterisk ,webrtc .I have experiences with webrtc ,asterisk ,etc
last month I successfully deployed webrtc phone solution (if you google : webrtc asterisk ,u can find) ,although it's open source ,it need knowlege of voip,asterisk ,webrtc to trouble shoot etc
I also reseached several famous open source webrtc solutions ,many webrtc conference solution are using voip /SIP to bridge with PSTN/mobile network