AT&T MERLIN LEGEND System Reference Manual page 315

Features
Privacy
Pools
Queued Call Console
System Access
System Programming
2-266 Personal Lines
When an individual personal line is assigned to more than one telephone, a user
with the personal line cannot join an in-progress call on which Privacy has been
activated.
A personal line cannot be assigned to a pool.
Personal lines cannot be assigned to a QCC.
When a call on a Personal Line button is transferred to another user, the call
rings on an Intercom or System Access button. The LED next to the personaI
line flashes (fast) to indicate that the call is on hold for transfer. If the call is
answered at an Intercom or System Access button, the LED next to the personal
line goes on steady. If the user shares the personal line appearance and
answers the call by using the Personal Line button, the call is removed from the
Intercom or System Access button.
Assign or remove personal lines to or from stations.
Extensions -> LinesTrunks
Assign or remove principal user of a personal line-specifies that an
individual extension can forward calls received on a specific personal line to
an outside telephone number; calls received on the personal line follow only
the individual extension's Coverage patterns and not the Coverage patterns
of other users who share the line.
LinesTrunks -> More -> PrncipalUsr