PGM 102, "System & Device IP", but I wouldn't use DHCP for the phone system.
I usually set "MFIM/E IP Address" to an IP Address of the customer's subnet. I'll then set the "Second System IP Address" to our own sub-net (Hopefully 10.10.10.x) and set the "Automatic IP Assign" to ON.
This allows the phone system to just take one IP address from the customer. The phone system then sends out IP addresses to the phones and gateways. Helps to keep you away from the local IT Guy's mess.
Sorry your customers don't have smart phones. Didn't realize you were running an interconnect for the technically challenged.
