AT&T MERLIN LEGEND Release 4.0 Feature Reference page 390

Feature Reference
Call Waiting
Coverage
390
Personal Lines
A user does not hear a call-waiting tone for calls received on a personal
line unless the business subscribes to call-waiting service from the local
telephone company.
Assigning a sender as the principal user of a personal line specifies that
the calls received on the personal line are sent to the principal user's
individual and group receivers. A principal user with remote call
forwarding can forward calls received on the personal line to an outside
number.
Calls received on personal line buttons programmed for No Ring or on
senders' extensions other than the principal user's are not eligible for
coverage.
If no principal user is assigned and the personal line is shared by other
senders, calls received on the personal line are sent to all available
Individual Coverage receivers for all senders sharing the line and to the
Group Coverage receivers programmed for the sender with the lowest
logical ID.
In Release 2.1 and later, a call answered on a personal line using a
Cover button can be picked up by anyone with a button for that
personal line. However, the picked up call cannot be transferred
because it is still considered to be on hold at the other extension.
Prior to Release 2.1, once a person answers a call received on a
personal line on a Cover button and puts the call on hold, the sender
and any other user who shares the personal line cannot pick up the call
by pressing the personal line button. For proper handling, the receiver
should transfer the call to the sender.
In Release 2.1 and later, calls received on personal lines with Do Not
Disturb on will go immediately to coverage instead of waiting for the
coverage delay interval.