Panasonic KX-TD500 System Reference Manual page 596

4.02 Automatic Callback-Station
Description
If busy tone is heard when calling an extension,
dialing "6" and hanging up causes Automatic
Callback to the caller as soon as the called party
concludes conversation.
When callback ringing for the caller starts,
answering by off-hook offers calling the other
party automatically.
Off-hook prior to the start of callback ringing
cancels this function.
Also no answer during four ring tones after the
start of callback ringing cancels this function.
Programming
None
Conditions
Up to four extensions are able to assign this
function to one extension at the same time.
The fifth extension attempting to set this function
is rejected by reorder tone.
If you do not dial "6" within 10 seconds after
hearing busy tone, you hear reorder tone and
cannot execute this feature.
Even if Call Forwarding-No Answer or Do Not
Disturb is assigned to the extension, the
extension user can set Automatic Callback-
Station: callback starts on the extension.
Automatic Callback-Station cannot be set by the
extension which has a call on consultation hold.
Operation
Setting Automatic Callback-Station
1. Lift the handset.
• You hear dial tone 1, 3, or 4.
2. Dial the directory number of the
other extension.
• You hear busy tone 1 or 2.
3. Dial "6".
• You hear confirmation tone 2,
4. Replace the handset.
Answering callback ringing
As soon as the other party concludes the
conversation, callback ringing starts.
1. Lift the handset .
• You hear ringback tone.
5-A-16
then reorder tone.
Calling the other extension
starts.