I was having intermittent problems with outbound audio on calls with my setup. I kept getting the message in the call log about RTP attempting to connect to IP 0.0.0.0--the same issue that many people have found where firewalls caused problems, but I didn't have a firewall enabled. My phone server has 2 NICs and one was connected to my data network for admin access. When 3CX started, it treated that as the main network, and so then all of my phones were trying to access a different network (though it was the same server.) Usually it worked ok, but about 1 call in 10 would have the problem. So I disabled the NIC connected to my data network and the problem is gone. So, if you have a machine with multiple NICs connected, you may want to watch that issue.