AT&T MERLIN LEGEND System Reference Manual page 279

Features
Signaling
System Access
Transfer
System Programming
2-230 Messaging
If a display telephone user presses a Signaling button only to send an audible
signal to a telephone with a posted message, the posted message at the
destination is not shown on the display. However, if a display telephone user
selects an Intercom or System Access button, lifts the handset, and uses the
Signaling button to dial the extension, the posted message at the destination
telephone is shown.
In the Hybrid/PBX mode, when a Shared System Access button is used to leave
a message for a display user, the extension shown is that of the telephone with
the Shared System Access button and not that of the principal station.
When a principal station user with an MLX display telephone posts a message
and a call is answered at the Shared System Access button, the calling
information is cleared from the principal station. However, the Home screen on
which the posted message is shown is not restored. If the principal station user
presses the Home button or makes or receives a call, the Home screen is
restored.
A non-display user who sends a message by using Leave Message while a
transfer to another telephone is in progress cannot determine who received the
message. For example, if station A calls station B and station B transfers the call
to station C, and if station A sends a message before the transfer is complete,
station B receives the message. If station A sends a message after station B
completes the transfer, station C receives the message even if station C does
not answer and the call is ringing at station B as a transfer return.
If an inside call is transferred to a telephone with a posted message, only the
display telephone user who transfers the call sees the posted message and not
the original caller even after the transfer is completed.
If a call is transferred to an extension programmed as a fax, the message
indication is not sent to the fax message-waiting receiver regardless of the
amount of time programmed for the fax message-waiting threshold.
Change or add posted messages.
More -> Labeling -> PostMessage
Assign a fax Message Waiting Reciever.
AuxEquip -> Fax -> Msg Waiting
Assign a Message Waiting Reciever for calling group.
Extension -> Grp Calling -> Message