AT&T MERLIN LEGEND System Reference Manual page 357

Features
Feature Interactions
Auto Dial
Automatic Route Selection
Conference
Display
Directory
Hold
Park
Privacy
2-308 Recall
Multiline telephone user in a Behind Switch system presses the Recall
button and is disconnected. The interval is too long and should be
decreased to 350 ms.
If a single-line telephone with a timed disconnect is used (for example AT&T
models 2500YMGK-PEC3178-NHL and 2500MMGK-PEC3101-ETR),
pressing the switchhook automatically disconnects the call. With this type of
telephone, the Recall button must be used instead of the switchhook for
features that require a switchhook flash (for example, Transfer or Hold).
Pressing the Recall button sends a switchhook flash and does not
automatically dial the last number manually dialed.
The Conference button is pressed to enter the Flash special character, which
simulates pressing a Recall button, in a telephone number programmed on an
Auto Dial button.
Recall cannot be used to hold onto an outside line if ARS was used to make the
call.
A singe-line telephone user with a Recall button can add a participant to a
conference call and connect all participants by using the Recall button. In
addition, the Recall button can be used to drop the most recently added
participant or to drop a busy number.
The Conference button is pressed to enter the Flash special character in an
Auto Dial, directory listing. Personal Speed Dial, or System Speed Dial
telephone number.
When an MLX display telephone user presses a programmed Recall button
while on an outside line, the line information is re-displayed as if the user had
gone off-hook.
The Conference button is pressed to enter the Flash special character, which
simulates pressing the Recall button, in a directory listing telephone number.
A single-line telephone user with a Recall button can press the Recall button to
put a call on hold.
A single-line telephone user can use Park if the telephone has a Recall button.
A single-line telephone user with a Recall button can use the Recall button to
activate or cancel Privacy during a call.