AT&T SYSTEM 25 Manual page 106

This feature applies to multiline voice terminals only.
Some multiline voice terminals have a built-in loudspeaker that allows on-hook dialing, group
listening, and monitoring of call progress signals. Pressing the SPEAKER button at an idle
terminal has the same effect as lifting the handset; the user is connected to the selected call
appearance and hears dial tone.
When using the handset, pressing SPEAKER will turn on the speaker to support the Group
Listen feature; pressing SPEAKER again will turn off the speaker and associated LED. Once
the user has lifted the handset, it is possible to return to "hands-free" operation only by
putting the call on hold, hanging up the handset, then reconnecting the call by pressing
SPEAKER. Hanging up the handset will terminate the call whether the speaker is on or off.
The built-in speaker provides one-way communication (listen only). The user
NOTE:
must pick up the handset to converse
Placing a Call Without Lifting the Handset
1 Press
The light next to this button turns on.
2 Dial the telephone number.
3 If the party answers, lift the handset and talk.
o r
If the party does not answer, press
to turn the speaker off.
Allowing Others to Listen
1 Press
The light next to this button turns on.
2 Use the handset to talk.
NOTE:
disconnected.
Speaker
and listen for dial tone.
[SPEAKER]
while on a call.
[SPEAKER]
If you hang up the handset, your call will be
again
[SPEAKER]
Speaker 2-93