AT&T MERLIN LEGEND System Reference Manual page 301

Features
Feature Interactions
Auto Dial
Barge-In
Callback
Call Waiting
Camp-On
Conference
2-252 Paging
If a loudspeaker paging jack is not programmed, Loudspeaker Page is not
shown as a feature choice on MLX display telephones.
Using the speakerphone for Speakerphone or Loudspeaker Paging may
create a feedback tone.
Any loop-start (LS) or ground start/loop start (GS/LS) line jack can be
assigned as a loudspeaker paging port. A line/trunk jack on an 800 DID,
100D, or 400EM (tie-trunk) module cannot be programmed as a loudspeaker
paging port.
Station jacks cannot be programmed as a loudspeaker paging port.
The loudspeaker paging port cannot be assigned to a pool that contains
trunks used to make or receive outgoing calls.
When a line/trunk jack is assigned as a loudspeaker paging port, only the
loudspeaker paging system can be connected.
If the loudspeaker paging system is multi-zone, users must dial the
appropriate zone number specified by the paging system before making an
announcement.
The system supports loudspeaker systems with "talkback" (bi-directional
paging), which allows users to respond to pages.
Loudspeaker pages cannot be made with MLC-5 cordless telephones.
A speakerphone paging group extension number can be programmed onto an
inside Auto Dial button.
Barge-In cannot be used to join speakerphone or loudspeaker paging calls.
A speakerphone paging (voice-announced inside) call that is queued by using
Callback automatically becomes a ringing call. Callback cannot be used for
calls to a speakerphone paging group. Systems with loudspeaker paging can
be setup to allow calls to be queued for the loudspeaker paging system by
placing the Loudspeaker paging port in its own pool and having users access
the paging system via the pool. When the pool is busy, the call to the
loudspeaker paging system can be queued.
Call Waiting cannot be used for Group Speakerphone Page calls to busy
extensions.
Camp-On cannot be used for calls to busy speakerphone paging groups.
Speakerphone and loudspeaker paging calls cannot be added to a conference.