TONES provide information about the progress of a call



DIAL TONE Continuous 2 Frequencies System is ready to accept digits
BUSY 1 sec on / 1 sec off Called number is busy
Fast busy (1/4 sec on/off)
Unavailable feature, facility, or unassigned code
SPECIAL DIAL TONE 3 short bursts of dial tone followed by continuous dial tone Feature activation started, ready for additional input
CONFIRMATION 2 short bursts of tone Requested feature has been activated
CALL WAITING 2 short bursts of tone at 10 sec intervals External call is waiting
CALLBACK- BUSY RECALL 3 short bursts of ring tone Busy station is now free