You may want to look into an NEC wireless system. I have installed many of these and have had nothing but great success. The NEC wireless system comes as a stand alone and can be interfaced with a Norstar thru Analog Ports. You would need and analog station module for the norstar and the NEC 2000 wireless system with the total handsets and ZT's deployed thruought your building. NEC wireless ususally prices out cheaper than that of the Companion.
I also work with the companion, and spectralink. These are also great products, however I am partial to NEC equipment and seeing as how I am certified on all three and have installs of all three, I hear and see that the NEC wireless sytem seems to work better.