Hi, I already tested three different softphones and all the audio fails when both people speak at the same time. Has anyone had this problem?
This could be related to bandwidth , codec selection , Jitter.
This article give you a more detailed cause about the problem
It might be very basic echo suppressor somewhere in the call path. I remember Zoiper had this problem few years ago (I don’t know if it still works the same), but if that are three different softphones then maybe this is something else, e.g. second call leg.