NEC DT330 User Manual page 21

1.
LED
Programmable Feature keys have a built-in Light
Emitting Diode (LED) that lights or flashes according to
the activity of that Feature key.
Function Key Activities
Feature + 0 = Side Tone On/Off. (for handset)
Feature + 1 = Turns microphone on or off.
Feature + 2 = Adjusts handset receiver volume.
Feature + 3 = Selects ringer tone.
Feature + 4 = Adjusts transmission/receiving volume.
Feature + 5 = Activates hands-free operation.
Feature + 6 = Deactivates hands-free operation.
Feature + 7 = Turns call indicator lamp on or off for
incoming call notification. (If turned off, this lamp will still
light to indicate message waiting.)
Feature + 8 = Turns Dynamic Dial Pad on or off.
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