This intercom Auto Dial button allows the user to access the voice messaging system with the touch of one button.
To program a Voice Messaging Auto Dial button:

Procedures
Programming a VMS Cover Button (F15)
Programming a Do Not Disturb Button (F01)
Programming a Voice Mailbox Transfer Button (F14)
Programming a Voice Messaging Auto Dial Button
(Intercom 777)
Programming a Station Lock Button (F21)
Programming a Record-a-Call Button (PARTNER ACS Release
3.0 or later) (F24)
Programming a Call Screening Button (PARTNER ACS Release
3.0 or later) (F25)