AT&T SYSTEM 25 User Manual page 8

Handset Tones
System 25 signals you with tones that are heard through the
handset. The tones and their descriptions are listed below.
DIAL TONE IIIIIIIIIIIIIIIIIIIIIIIIIIII (a continuous steady tone)
You can dial.
CONFIRMATION TONE III III III (three short tones)
Your action is accepted. Proceed to the next step.
RINGBACK TONE IIIIIIIIIIIII IIIIIIIIIIIIII IIIIIIIIIIIII (repeating
On/off tone)
The number you dialed is ringing.
SPECIAL RINGBACK TONE IIIIIIIIIIIIIII III (one long tone
and one short, dull tone)
The person you dialed has Call Waiting.
BUSY TONE IIIIIII IIIII IIIIIII (repeating on/off tone)
The number you dialed is busy.
FAST BUSY TONE
The number or access code you dialed is busy, restricted, or
misdialed.
QUEUING TONE
Your callback request for a busy station or outside line has been
confirmed.
DEQUEUING TONE IIII III III
The station or outside line that you requested is available, and
your call can now be completed.
4
IIIII IIIII IIII (repeating on/off tone)
IIIII IIIII IIIII IIIII IIIII (five short tones)
(three short tones)