I installed the 3CX Phone System some weeks ago and it works fine as long as the clients are on the same network/the same router. What I'd like to do is to allow people to connect from external networks. Here my problem begins. My external clients (those that are not on my internal network) can call each other but they hear nothing. I think the only solution is to use the new client - VOIP Client - 4132 because it allows you to login to SIP server (authentication type under login config). 3CX phone system authentication (under login config) does not work, because each client logs in with it's internal IP. I opened the ports on firewall: 5060 7000 - 7499 9000 - 9009 External client has the following port settings: SIP port: 5060 First RTP port: 7000 Last RTP port: 7499 The 3CX Phone System has the following settings: SIP Port: 5060 Ports to use for internal calls: 7000 - 7499 Ports to use for external calls: 9000 - 9009 It's said for the Ports to use for external calls (9000 - 9009) These ports will be used for calls placed via VOIP providers. Assuming your phone system is behind the firewall, you will need to open these ports on your internet facing firewall. To check if the ports are open through the firewall, please run the firewall checker test by clicking on the button below "Firewall Test". Monitoring the network I found the external client does something on port 9000. Should I set the range First to Last RTP port on client as 9000 - 9009 instead of 7000 - 7499? Is there something else I should be carefull about?