AT&T MERLIN LEGEND System Reference Manual page 285

Features
Single-Line Telephones
Mode Differences
Hybrid/PBX
Key and Behind Switch
Considerations
2-236 Multi-Function Module
A single-line telephone or other type of tip/ring device can be connected to the
MFM and used to make and receive inside and outside calls.
When the Ringing/Idle Line Preference is activated and Automatic Line Selection
is set to select a System Access button, an outside line can be selected by
dialing the pool dial-out or Automatic Route Selection code.
When the Ringing/Idle Line Preference is activated and Automatic Line Selection
is set to select an Intercom button, an outside line can be selected by dialing
the Idle Line Preference code (usually a 9).
When both the MLX telephone and the device connected to an MFM are in
use, the Voice Announce to Busy feature cannot be used to reach the MLX
telephone user.
The system cannot distinguish between tip/ring interface and SAA operation;
the operation is selected by using pin straps in the MFM.
When the MFM is in tip/ring interface operation, only DTMF devices can be
used.
When the Ringing/Idle Line Preference for an MFM device is activated and
Automatic Line selection is set to an outside line/trunk, inside calls cannot be
made and features cannot be used. Both inside and outside calls can be
received.
Calls are independently sent to the MLX telephone and its associated MFM.
The following should be used when the user wants calls received at the MLX
telephone to also be directed to the device connected on an MFM:
Cover buttons
Shared System Access buttons (Hybrid/PBX only)
Buttons assigned the same outside lines
Forward/Follow Me
Transfer
When the connected device is used by the MLX telephone user to provide
supplementary answering (such as an answering machine) or ringing (such
as an external alert) only for calls received on personal lines, and lines/trunks
are assigned to or removed from the associated MLX telephone, the
lines/trunks should also be assigned to or removed from the MFM.
An MFM cannot be assigned as a system operator position.
An MFM can be assigned as a calling group delay announcement or as a
calls-in-queue alert for a calling group queue.