If the extention you want to program is a display phone, when the KT is idle/on-hook, press FEAT, #, 9 then the button you want to assign. The diplay will show how the button is programmed. If it's programmed as a call coverage button, use the advice Jadix provided. If not, determine which key pattern is assigned to the KT in Class 10, Item 12. If you want to program an attendant phone, look for the pattern in Class 15. If it's a regular extention, find it in Class 14, program the button for call coverage immediate, delay or no-ring.