AT&T MERLIN LEGEND System Reference Manual page 169

Features
Normal Call-Handling
Operation
2-120 Direct Station Selector
Normal call-handling operation is in effect when the position is not in supervisor,
message status, or hotel Extension Status operation. The DSS buttons are used
for one-touch dialing of extension numbers. When a button for a user extension,
calling group extension. or paging group extension is pressed, the extension
number is automatically dialed. In the Hybrid/PBX mode, the system operator
can either select a specific pool or dial the ARS code by pressing the DSS
button for a pool dial-out code or ARS code. If a DSS button for any of the
extensions or codes mentioned above is pressed before the handset is lifted,
the speaker is automatically turned on and an Intercom or System Access
button is selected.
When a DSS button is pressed for a user extension that is "high and dry" (the
user is not active on a call and is not listening to dial tone), a signal (beep) is
sent to the user's telephone.
A system operator can also use a DSS button to activate a feature that requires
an extension number—Barge-ln, Conference, Send/Remove Message, Forward
(including Remote Call Forward), Follow Me, Leave Word Calling, Reminder
Service, and Transfer. To do this, the system operator presses the programmed
or fixed feature button, or presses the Feature button and dials the feature code,
and then presses the DSS button for the extension number.
The result of pressing a DSS button while on a call depends on the type of
system operator position, the type of button pressed, and how the system is
programmed for transfers (see Table 2-5).