AT&T System 25 - Manual (Page 54)

Placing Calls (Continued)
Using Facility or Pers Line Buttons
1 Press and listen for dial tone.
2 Dial the telephone number or press a button.
Requesting Busy-to-idle Reminder
If all outside lines are busy when you try to place a call, you can
request a Busy-to-Idle reminder and be notified when a line is
available.
1 Do not lift the handset.
2 Press
Your telephone will ring once when a line is available.
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