NEC DTL-6DE-1 - DT310 - 6 Button Display Digital Phone User Manual page 28

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 = Selects between Normal, Dynamic Dial
Pad, and Preset Dial.
Note: * indicates the services which are not available
for DT700 Series.
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