I need to integrate Cisco 3825 with PBX (Iwatsu). PBX vendor advise me to provide 1x 4 Port FXO card to connect to PBX 4 Port FXS card.. another 1x 4 Port FXS card to connect to PBX 4 Port FXO card. We have about 30 analog phones at the PBX system. I need both way communication between the cisco IP phone and 30 analog phones. Any idea do this work?