I have Jami installed but I rarely use it. I decided to try today, when I call a contact, the call is immediately failed. I am on GNU/Linux, Debian, using the last version from Jami repository.
I tried with the F-Droid version from Android, same result.
My friend called me from his iPhone, Jami on the computer rang and I could answer and the call was working. After that, I can call him for a little while, then it does not work anymore, I have the failed call immediately again.
For these tries, we are both connected to the same local network (phone with wifi, computer ethernet, DHCP address allocated by the same server).