AT&T MERLIN LEGEND System Reference Manual page 407

Features
Night Service
Paging
Park
Personal Lines
Pickup
Privacy
Queued Cell Console
Recall
Reminder Service
2-358 System Access
In the Hybrid/PBX mode, Night Service calls override any ring options (Delayed
Ring or No Ring) programmed for System Access buttons and ring immediately.
On Shared System Access buttons, Night Service calls follow the programmed
option (Immediate Ring, Delayed Ring, or No Ring).
Announcements using Speakerphone Paging can be made from a Shared
System Access button when a system operates in the Hybrid/PBX mode.
However, users cannot join a page (as they can other calls) on Shared System
Access buttons.
When a user parks a call made or received on a System Access button, Shared
System Access buttons do not ring when the parked call returns.
When a call on a Personal Line button is transferred to another user, the call
rings on an Intercom or System Access button. The LED next to the Personal
Line button flashes (fast) to indicate that the call is on hold for transfer. If the call
is answered at an Intercom or System Access button, the LED next to the
Personal Line button goes on steady. If the user shares the personal line
appearance and answers the call by using the Personal Line button, the call is
removed from the Intercom or System Access button.
If the Pickup feature is used to answer a call ringing at a System Access or
Shared System Access button, the call is removed from the ringing telephone
and moves to the System Access or Shared System Access button used to pick
up the call. The green LED goes on next to the Intercom or System Access
button used to answer the call and next to all Shared System Access buttons
programmed for that specific button.
In the Hybrid/PBX mode, if Privacy is activated on the principal station for a
System Access button or by another user with a Shared System Access button,
other users, including the principal station, cannot join the conversation. If
Privacy is activated after another user joins the conversation, it does not affect
that person, but no other users can join the conversation.
System Access buttons are not assigned on a QCC. The QCC system operator
uses Call buttons to make and receive inside and outside calls.
Recall can be used on ringing (unanswered) inside calls when the call is made
on an Intercom or System Access button. it cannot be used on an Intercom or
System Access button when the user reaches a busy extension.
A Reminder Service call overrides programmed ringing options (Delayed Ring
and No Ring) and rings at the principal station. Reminder Service calls do not
ring at Shared System Access buttons.