AT&T MERLIN LEGEND Release 4.0 Feature Reference page 278

Feature Reference
Ringing Options
Signaling
SMDR
System
Access/Intercom
Buttons
System Numbering
Transfer
278
Group Calling
Abbreviated Ring is not operable for calls to the calling group extension
because a calling group member active on a call is considered
unavailable for incoming calls. In Hybrid/PBX mode, calling group
members should program SA buttons for Immediate Ring.
A Signaling button cannot be programmed for a calling group.
In Release 2.0 and later, calls to calling groups are associated with the
most recent extension to handle the call; that is, if a call is transferred to
a calling group, the calling group extension appears on the Station
Message Detail Report (SMDR). If the call is answered by the calling
group delay announcement device, the extension for the device is
recorded on the SMDR record, but it is overwritten if the call is
answered by a calling group member.
Timing begins as soon as the calling group member or delay
announcement device answers the call. If the caller hangs up while
listening to a delay announcement, the call is associated with the
extension of the answering device.
Calls to a calling group ring on SA or ICOM buttons on the telephones
of calling group members. A calling group member who is making or
receiving a call on a Shared SA button is considered unavailable by the
system; the principal owner, however, is considered available and can
still receive calls directed to the calling group.
Extensions for calling groups (the factory-set extensions are 770–791
and 7920–7929) are assigned and can be renumbered through system
numbering.
A call transferred to a calling group is not returned to the originator; the
call is handled like any other call received in the calling group. For
example, the system follows the same hunt sequence to locate an
available calling group member, and the call is eligible for a delay
announcement if one is programmed. A calling group member who has
a call on hold for transfer is considered available for a call, since
transfer hold requires pressing the Transfer button rather than the Hold
button.
Voice-announced transfers cannot be made to a calling group. There is
no limit to the number of calls that can be transferred to a calling group.
In Release 2.0 and later, when an inside caller is transferred to a calling
group and no members are available, the inside caller hears a 1-burst
ringback. When an outside caller is transferred to a calling group and
no members are available, the outside caller hears a 2-burst ringback
or Music On Hold (if programmed).