Two SIP listening ports for single Asterisk

There is no way to make a single instance of Asterisk listen on multiple ports. However, you can use an iptables REDIRECT to achieve the same functionality.

To redirect a single port with iptables:

 iptables -t nat -A PREROUTING -i eth0 -p udp --dport 5062 -j REDIRECT --to-ports 5060

This example redirects UPD port 5062 to port 5060, which effectively allows Asterisk to listen on both of them. Remember to save the rule so that it survives a reboot.

From: http://lists.digium.com/pipermail/asterisk-users/2008-November/221970.html