AT&T MERLIN LEGEND Release 4.0 Feature Reference page 398

Feature Reference
System Access/
Intercom Buttons
Transfer
398
Pickup
If Pickup is used to answer a call ringing at an SA or Shared SA button,
the call is removed from the ringing telephone and moves to the SA or
Shared SA button used to pick up the call. The green LED turns on next
to the SA button used to answer the call and next to all Shared SA
buttons programmed for that specific button.
An inside call ringing at an SA or Shared SA button can be picked up
at another telephone. All associated SA and Shared SA buttons go idle.
A transferred call can be answered by using Pickup.