AT&T System 25 - Manual (Page 47)

Message Waiting
Message Waiting is available on most multiline telephones, and
is a feature that can be used by anyone in the system. Most
telephones have a light that indicates a waiting message.
You may also have a button, which you can press to
turn the light off after you receive messages. If yor telephone
does not have a button, you must use a feature access
code to turn it off.
If you have a button, you can also control the
message waiting lights on telephones that you provide
Individual Coverage for, or for which you have a
button, (if you want to check on the feature)
associated with the button, go to the section titled
"Personal Message Waiting".)
Turning On Message Lights
1 Listen for dial tone, then press
2 Dial the extension number of the other telephone.
3 Listen for confirmation tone, then hang up.
NOTE: If you hear fast busy tone instead of confirmation
tone, either the other telephone has no message waiting light
or the extension you dialed is invalid.
Turning Off Message Lights
1 Listen for dial tone, then press
NOTE: To turn off your own light, press your
button.
2 Dial the extension number of the telephone.
3 Listen for confirmation tone, then hang up.
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