I personally would avoid that Kurun, if I were you. It is an over-complicated setup that in fact is unnecessary.
You could have 10 SIP devices (ATAs, IP phones, and softphones) on your LAN at 10 different IP addresses, and each and every one of them could be using ports 5060 and 16384-86, and the router would sort it out just fine. All the devices (or computers) could get their local IP addresses assigned by DHCP to boot and it would still work itself out. That's the power of STUN and NAT routing. What happens is that to the outside WAN world 192.168.1.
3:5060 would become something like 212.54.78.201:60445 and so even if you had a second device that was at 192.168.1.
4:5060 it would be assigned something like 212.54.78.201:61225. In other words, there is more than enough port 5060 to go around when using a NAT/PAT router since all the ports get changed anyway to something else.
Network address translation - Wikipedia, the free encyclopedia
Port address translation - Wikipedia, the free encyclopedia