Alow me to start off by saying I am not a tech, but can very somewhat technical. I am planning to install a Valcom V-9941A single zone talkback paging unit. It will be used with a talkbackhorn and a dedicated phone line (3rd line of a 3 line tele) I want to use the "inhibit" feature to allow it to disconnect talkback speakers when a second telephone is picked up, but says I need to have a single line telephone modified for "A" lead control. I have no idea what this means. Can I make any phone "A" lead control capable? The link is for the manual of unit I am using. Note the inhibit option Installation instructions for V-9941A