Panasonic KX-TD816JT Features Manual page 223

<Tone>
Tone to held line
Conference
(by intrusion)
Conference
<Ring Tone>
Outside Calls /
Outside Call Hold Recall
Intercom Calls /
Intercom Hold Recall
Timed Reminder /
Callback Ringing
(Camp-on Recall)
Tone / Ring Tone
1 s
1s
10 s
223