That's odd that it is acting as if the phone is unplugged... not just in a busy state. I agree with Voyager that a hook-switch may be part of the problem and absolutely that you should switch out the phone. If switching the phone and or replacing the hook-switch don't work, I would make someone else the owner of that PhDN.

- Tony
Ohio Data LLC
Phone systems, data networks, firewalls and servers in Central Ohio.
Some people aren't used to an environment where excellence is expected.