I have the same issue. I have been through extensive testing with my VoIP provider.    After many days and hours of testing multiple SIP devices, their response below;   "Not sure if you are using TPG, recently, some of our clients on the TPG NBN connection had a similar issue - no incoming voice. In all cases, we were sending RTP to the client's side, but they didn't receive it. It wasn't a TPG outage, we had 4 or 5 clients. Please raise a ticket with your ISP and check."   Our Firewall requirements - https://www.voipline.net.au/support/article/360001084436-Firewall-Requirements   I will follow up with TPG support.. ... View more