First off, thanks for being here, this is a great place for information.
This issue is a result of the wonderful health hysteria currently happening. We are having to consider having our techs work remotely from home. We presently run Yealinks internally on CHAN_SIP and want to put in a set of softphones on home PCs/Mobiles. We have created secondary extensions for these softphones.
Our Phones run on a dedicated 10.x network to the EGS Gateway unit owned by the SIP Trunk provider. The Main FreePBX has dual NIC, one fo rthis phone network, and one for the business network so we can admin and use voice mail etc. Now I am testing on my Android using Mizudroid. We setup a firewall rule (SonicWALL) for 5160/5161 and 10000-20000 UDP and a NAT policy to match to send those ports to the phone server.
I can get the softphone to register and authenticate via the internet and business IP (not the dedicated 10.x network), and we can even dial extensions between the desk phones and the softphone in both directions, but once connected, we get no audio. I checked the codec on the softphone and is matches the preferred one in the server.
We are running FreePBX 18.104.22.168 on Asterisk 16.6.2