Intercom feature I need help fixing the intercom feature on my RCA phones. They used to work.

Intercom referred on page 10 Intercom referred on page 10

INTERCOM CALLS .................................................................... 15
ONE-TOUCH INTERCOM ............................................................. 15
ANSWERING AN INTERCOM CALL .................................................... 16
INTERCOM HOLD ...................................................................... 16
INTERCOM CONFERENCE CALLS ......................................................... 16 INTERCOM CALLS .................................................................... 15
ONE-TOUCH INTERCOM ............................................................. 15
ANSWERING AN INTERCOM CALL .................................................... 16
INTERCOM HOLD ...................................................................... 16
INTERCOM CONFERENCE CALLS ......................................................... 16