I have been assigned to work on this old Panasonic system. I have not seen it before. All the customer wants is to take the ringing off of one phone. They want the lines to appear, but not ring. I downloaded the manuals, it seems that I can program this directly at the set in question, theyr is a way of programming the co keys to ring a certain way (Program 99...etc) but it changes the ringing ,it does not shut it off. the phone system is a SuperHybrid KX TD-308 and the phone is a kx-t7220 PDX