Is there a definitive guide as to how to setup remote extensions on the IPPBX 2820? I have looked at the faq section and the link does not go anywhere.

I have a remote phone registed (which is the other side of another firewall) and can make a call but get no audio.

Any clues? Do I need to perform any port mappings on the IPPBX?

Thanks.

If you still have the issue, try making a LAN to LAN VPN between the two sites. Worked very well for me. Registers Cisco 504 phones and my Samsung GS2 with CSIP simple. Audio very clear both ways. I have Vigor IPPBX 2820 in office and Vigor 2820vn at remote. The GS2 auto registers as same extension whether I am in the office or on remote site.