I have an old 818 Digital Key BX. We lost a switch during a recent move. It had 4 buttons on it and an RJ-11 jack on the side. It was attached to the phone system and allowed me to select 1 of the 4 lines we had going into the KSU. I could then attach an analog phone to the RJ-11 jack and make or take calls on that 1 line that is selected. Does anyone know what that was called and possibly where I can get another? Thanks in Advance.