Maybe this will help. Since you are using remote hard IP phones via ISP service they are DHCP so the IP address will change eacgh time they log on. You can possibly use a public DNS server to dial by URL to reach remote agents. The H.323 standard does not support dial by URL. The SIP protocol does diaL by URL. Ping Tel makes SIP phone so you may want to contact them. I am not fasmiliar with you application but if you go through a NAT router then you will experiencv one-way speech due to dynamic port assignment to the subnet client. I don not work for Ping Tel but have played around with them in our lab at Samsung Telcom. They would be glad to speak with you.