Our second office is getting redone and we will need a doorphone linked to our IP Office system. The problem is that this site doesn't have its own IP Office box. The IP Office is in our main office and is connected to the other site via VPN. We already have a number of phones there so we know this method works. From my searching most doorphones require a direct connection to one of the analog ports on the actual IP Office. I have seen a few that are ethernet based and act as a SIP extension. Would these work with our system configured the way it is? I've used SIP over VPN for polycom phones, so I know that works, but I haven't worked with doorphones on IP Office before, so I don't know if it will work the same way.