Ahhhhhh, I understand what you are trying to ask now. You have a WAN connection between 2 sites, 1 with IPOffice and one with a legacy PBX and you want to do h.323 trunking.
You have 2 choices. Buy 2 voip gateways (such as multitech multivoip -
www.multitech.com) or buy 1 voip gateway for the non IP Office location, install a VCM5 card in your IPOffice, and purchase a 3rd party IP endpoints licence. Since your integration will be limited by the voip gateway anyway, it's probably cheaper to buy 2 voip gateways.
Or better yet, get the remote location to upgrade to IP Office.
Peter