AT&T MERLIN LEGEND Calling Group Supervizor's Manual page 26

Calling Group Supervisor Telephones
Phones with ICOM Buttons
ICOM Ring. Use this button to make ringing inside calls.
You can receive inside calls, calls to the calling group, and
outside calls transferred to you on this button; however, you
cannot make outside calls on it.
ICOM Voice. Use this button to make voice-announced
inside calls; your co-worker hears your voice over his or her
speakerphone instead of the phone ringing. You can receive
inside calls, calls to the calling group, and outside calls
transferred to you on this button; however, you cannot make
outside calls on it.
2-12 Buttons on Your Phone