Although it has been mentioned before I could not find the solution yet, please help me with the following: Running Win2008R2 server, one card connected to the internet with IP and domain name, one card connected to internal network. Firewall and NAT/Routing is done on the server. Internally everything works fine. I have it connected to some VOIP providers and analogue systems, those work fine too. When I connect an external phone, 3CX softphone/ 3CX iphone app to the server it registers fine and quick. It can call an extension and the person on the internal network can hear the external one but not reverse. External caller does not hear local. I have run the firewall checker, everything fine. IN the settings I have SIP port 5060 and reserved for external calls 9000-9004 (only two people using one line) I left the STUN servers at stun3.3cx.com / stun2.3cx.com port 3478 IN the firewall I opened all ports, set the router to forward all ports to the server. VOIP 5060 TCp and UDP forwarded, 9000-9004 UDP forwarded all open on firewall, incl STUN ports etc. I am out of options.... Suggestions welcome!