copied from: http://www.freepbx.org/support/documentation/howtos/howto-setup-a-remote-sip-extension This HOWTO assumes that your FreePBX system is sitting behind a NATed firewall with no direct connection to the outside world and it is NOT in the DMZ zone. If you are relying on this article to set-up your system, DO NOT place your system on a public IP address or a DMZ zone. This article does not address the potential security implications involved in such a setup. The four key considerations in setting up remote extensions are: 1. Ensure that your PBX is as secure as it can possibly be 2. Configure Asterisk so that it knows which IP addresses are inside your network and which ones are on the public internet 3. Forward the required ports from your firewall to your PBX 4. Configure the Extensions for External Use In order to accomplish the above we need to apply some configuration information into FreePBX, some Asterisk configuration files and on your firewall...