Step 1) Assign the Pool to the sets.
Step 2) Under Centralized Programming for the extension, First, touch that Button and Dial *35 (Turn off the ringing)
Step) 3) Still in Cent Prog, Touch the button again, Dial *14, touch it again, then the 3 intercom buttons, one at a time. Then PRESS ENTER.
*14 Sets the IDLE LINE SELECTION