Thanks for your reply. I did think it would require its own IP on each end, and I presume it would have to be in front of any firewall.
I didn't want to state it has to have a VPN, and someone comes in and say it doesn't.but I think I will recommend one is in place.
I presume any system with a fixed IP address will work, but Panasonic say you need one, I suppose a VPN is more reliable and if the system link goes down, it is the VPN and not the systems fault
His current system has to be upgraded as well, but the savings will be in using the 15-16 telephones he has on the old unit
Thanks again
Ken