AT&T MERLIN LEGEND Release 4.0 Feature Reference page 356

Feature Reference
If a user presses the Speaker button before lifting the handset, the system
selects a line and the user can dial a number. The microphone is muted, and
the user must lift the handset to speak to the person being called.
Telephone Differences
Queued Call Consoles
The microphone on a QCC cannot be disabled.
Other Multiline Telephones
Microphone Disable cannot be assigned to analog multiline telephones.
Single-Line Telephones
Microphone Disable cannot be assigned to single-line telephones.
Feature Interactions
Auto Dial,
Last Number Dial,
and Saved Number
Dial
HFAI
Paging
Transfer
Voice Announce to
Busy
356
Microphone Disable
Pressing a programmed Auto Dial, Last Number Dial, or Saved Number
Dial button turns on the speakerphone so the user can hear the number
being dialed. However, when an MLX telephone user's microphone is
disabled, the user must lift the handset to talk once the call is answered.
Users whose microphones are disabled cannot use HFAI to respond to
voice-announced calls. Pressing the HFAI button does not turn on the
LED or activate the feature.
Calls made to speakerphone paging groups can still be heard over
telephones whose microphones are disabled.
Calls can be transferred with a voice announcement to users whose
microphones are disabled, but the users must lift the handset to talk.
Users who are on their telephones and whose microphones are
disabled can still hear a voice-announced call over the speakerphone.
They must press the button with the incoming call and use the handset
to talk to the caller.