AT&T MERLIN LEGEND Release 4.0 Feature Reference page 102

Feature Reference
Paging
Park
Personal Lines
Pickup
Reminder Service
Remote Access
SMDR
System Access/
Intercom Buttons
Transfer
102
Callback
Callback cannot be used for calls to a speakerphone paging group. A
voice-announced inside call that is queued using Callback
automatically becomes a ringing call. Systems with Loudspeaker
Paging can be set up to allow calls to be queued for the Loudspeaker
Paging system by placing the Loudspeaker Paging jack in its own pool
and having users access the paging system through the pool. When the
pool is busy, the call can be queued.
Calls waiting in a callback queue cannot be parked.
The Callback feature cannot be used to request a busy personal line.
See "Line Request."
A callback request cannot be picked up at another extension.
Reminder calls cannot be queued by using Callback.
Remote access users can use Callback if the system is programmed for
remote access Callback (Autoqueuing). The user cannot hang up but
must wait on the line until the extension or trunk pool is available. The
caller hears Music On Hold if it is programmed.
SMDR begins measuring the duration of callback calls when the call is
completed.
Callback can be used on SA and ICOM buttons. When Callback is used
on an SA button, the call rings and the green LED next to the button
flashes only at the telephone that originated Callback. If a user other
than the person originating the callback call selects the SA button (with
a flashing LED) with a queued call and lifts the handset, the person
hears the queuing tone and the green LED on the originator's telephone
goes from flashing to steady. If the second person hangs up, the green
LED on the originator's telephone goes back to flashing and the system
directs the callback call to the originator. If the second person stays on
the line, the system directs the call to the second person and not to the
callback originator.
A call can be manually queued (Selective Callback) from an SA or
Shared SA button. The green LED next to the button at the telephone
that originated Callback and all those next to other related SA and
Shared SA buttons remain on.
A queued callback call cannot be transferred, but calls transferred to
busy extensions are eligible for Callback. When a user reaches a busy
extension while transferring a call, he or she can use Automatic
Callback or Selective Callback to queue the call before completing the
transfer. The caller hears ringback or Music On Hold (if programmed)
as with any transfer. When the extension is available, the call is
transferred to the extension automatically. If the extension is not
available before the transfer return interval expires, the call is removed
from the callback queue and returned to the transfer originator.