AT&T MERLIN LEGEND System Reference Manual page 231

Features
2-182 Group Calling
As calls come into the calling group, the system hunts for an available group
member in a circular or linear manner (see "Hunt Type" in this section). If a
group member is available, the call rings on a System Access or Intercom
button. If all group members are busy or otherwise unavailable, calls are held in
a calling group members become available, the calls are distributed
queue. As
on a first in/first out basis.
Inside callers who are transferred to the calling group hear a regular ringback
when all calling group members are busy and the call is sent to the calling
group queue; outside callers hear ringback or Music-On-Hold if it is
programmed for the system. In addtion, an announcement device can be
assigned to the group to play a recorded announcement to each waiting caller
in the order that the calls arrive in the queue.
Calling group members log in when they are ready to take calls ("available
status") and log out while they finish call-related activities or when they leave
their positions ("unavailable status").
Calls are sent to a calling group member only if the member is logged in and is
not busy on another call. When the Group Type is set to Auto Logout (the factory
setting), if a call is sent to a calling group member and is not answered within 30
seconds (5 rings), the call is sent to another member or to the front of the queue
if another calling group member
out the station where the call went unanswered and makes it unavailable for
subsequent calls until the calling group member logs in.
A calling group member is considered available if all of the following conditions
are met:
The station is signed into the calling group (available status).
The station is on-hook (handset is down or headset user disconnected the
last call and no red LED is on at the telephone) and the speakerphone is off.
The station is not ringing or busy on another call.
The station does not have a call on hold.
The station is not transferring a call.
The station is not in the program or test mode.
A System Access or Intercom button is available for call delivery.
Do Not Disturb is not activated.
Calls are not being forwarded via Forward, Remote Call Forward, or Follow
Me.
The calling group member did not activate Callback to reach a busy trunk
(Hybrid/PBX only) or extension.
The system is not calling another user who activated the Callback feature to
reach the calling group member.
not available. The system automatically logs
is