Also check that your router/firewall is set to forward the RTP port range (default is UDP 10000-20000) to the PBX.
If you still have trouble, capture traffic with tcpdump to see whether RTP is going out to the correct IP address and port.
Also check that your router/firewall is set to forward the RTP port range (default is UDP 10000-20000) to the PBX.
If you still have trouble, capture traffic with tcpdump to see whether RTP is going out to the correct IP address and port.