Asterisk + 2 NIC cards + Shorewall

it was a firewall rule error

You are running the firewall on the same box? Stop the firewall or iptables (if that is what it uses) and see if your problems go away.

Sure the problem will go away without the firewall, but there are reasons for the firewall to be there, so I need it to to work with this configuration.

Well you made the assertion Asterisk was not listening.

You have not configured your firewall properly.

If you dump your iptables chains somebody will help you with it.

External firewalls are the way to go. If you must run it on the PBX I wind that APF is the simplest firewall to install and configure.

Of course if you are going to open TCP/80 or UDP/5060 to any host on the Internet you might as well not bother with a firewall.