register with a g/k and you should be ok or redirect all ports to the tenor but have to change ext. IP everytime the public side changed. we have many customers registered to our softswitch from behind a firewall with a private IP and DHCP’d public IP and they are working just fine. only problem we have expereinced is that when a new IP is issued by the ISP’s DHCP server, it will take the quintum 3-5 minutes to re-register itself before anyone can make a call.