said by jwes :Our equipment is pure ISDN. There are 3 cables that plug into the ISDN wall socket.
I was thinking about what you said here and from what I remember, these ISDN teleconference units use 3 ISDN lines -- hence the three cables.
Your best solution may be to discard the ISDN based system and go to an IP based videoconferencing system. What kind of expenses are you currently incurring with the ISDN lines and how much are they wanting for the ISDN bridge service?