
Sally.
Please complete your profile so we may know who we are assisting.
Depending on what the telco can offer, the OPX of a single line set as an extension could be possible. This would allow you to be a intercom station, use the VM (if available) have calls transferred, etc., anything you could do if you were a single line station on site.
Without some type of a carrier system a KXT 7736 cannot work (I am not familiar with the type circuit you mentioned from the telco).
As far as VoIP, if you have a vacant CO port, use it with a gateway.
Hopefully I have not led you astray --- perhaps you might post in the ViOP or Networking forums for better advise on those areas.
Good luck, and I hope you enjoy the forum.