I am trying to connect an old Pingtel Express PX-1 phone in my lab. I am trying to connect to a 3CX system. Unfortunately, we bought this phone on ebay and it came with NO intructions, no user guide, nada. AND, I have been unable to find anything on the internet relative to set up of the phone. My problem is that it will not register to the 3CX. I can ping the phone and I can log into it and make changes, but nothing seems to work. Any suggestions??