I've seen a similar setup, where a school did this themselves with an Avaya Partner system. They thought they would have access to multiple phones, multiple lines. From what I could tell, they ended up using the common TR from the key system,so only one line at a time could be used. Once a line was used at a station, noone else could access any line or any other station.
More specific information would be needed to make a more qualified guess.
