I doubt, that it’s a firewall issue, because this behavior is happening also in LAN.
Our Pascom instance, all yealink telephones and the mentioned various softphones are situated in the same local network.
We are having this audio problem only on outgoing (even internal) calls with the softphone clients (to any hard- or software device).
Incoming calls to softphones (from any device) are working (all in LAN).
Incoming or outgoing calls with yealink phones are working properly.
With the mobydick softphone (Classic client), all audio is working as expected, but when i use the new Pascom Client on the same device, the issues still persist as described above.