AT&T MERLIN LEGEND Release 3.0 Programming Summary Manual page 39

Idle States
When the system is forced idle, the following occurs: multiline telephone users
hear a signal, indicating that the telephone cannot be used; display telephone
users see the message Wait: System Busy; single-line telephone users do
not hear a dial tone.
Line or Trunk Idle
Since these procedures require the line or trunk to be idle only at the instant of
programming, the line or trunk is not forced idle (as described in the previous
paragraph). The following procedures can be performed only when the line or
trunk being programmed is idle:
Identify loudspeaker paging extension jack.
Assign trunks to pools.
Specify incoming or outgoing DID or tie trunk type.
Specify tie trunk direction.
Specify tie trunk E&M signal.
Extension Forced Idle
When a telephone or data terminal is forced idle, no calls can be made or
received on that telephone or data terminal. The following procedures can be
performed only when the telephone or data terminal being programmed is
idle:
Assign call restrictions.
Assign pool dial-out restrictions.
Copy extension assignments.
Assign lines, trunks, or pools to extensions.
Assign labels to a personal directory.
Use centralized telephone programming.
Programming Basics 1-13