AT&T MERLIN LEGEND System Reference Manual page 284

Features
Telephone Differences
Multiline Telephones
When the Automatic Line Selection sequence is set to select an Intercom or
System Access button, an outside line can be selected by dialing the Idle
Line Preference code (usually a 9--for Key and Behind Switch) or by dialing
the pool dial-out or Automatic Route Selection code (Hybrid/PBX only). If
Automatic Line Selection is set to select an outside line button before an
Intercom or System Access button is selected, the device cannot be used to
make inside calls (inside calls can be received only). Additionally, the
following features cannot be used:
Personal Speed Dial
System Speed Dial
Account code entry
Pickup (individual and group)
Forward/Follow Me
Privacy
Reminder Service
Log in and out of calling group
Note. The features Forward and Follow Me (including Remote Call Forward)
and Privacy are not recommended for use because the user does not have
an LED that indicates when the feature is active.
Ringing options should be set to No Ring for each outside line on which calls
will not be received.
When the device is used for 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.
When the device is used for both inside and outside calls to supplement
ringing (external alert) or to answer or screen calls (answering machine),
calls can be redirected to the device by assigning a Primary Cover,
Secondary Cover, Group Cover, or Shared System Access button
(Hybrid/PBX only). In addition, the MLX telephone user can activate the
Forward/Follow Me features to redirect incoming calls to the device.
However, Coverage and Foward/Follow Me should not be used
simultaneously.
On any multiline telephone, an inside Auto Dial button can be programmed to
determine whether devices such as fax machines or modems connected to
the telephone via an MFM are in use.
An MFM can be installed only in MLX telephones and cannot be used with
analog multiline telephones.
Multi-Function Module 2-235