Panasonic KX-TD500 System Reference Manual page 477

7.00 Call Waiting
Description
Call waiting tone to a busy extension indicates
that another call (extension or CO line) is waiting.
To assign or cancel this function, dial the feature
number for "Call Waiting Set" or "Call Waiting
Cancel".
Programming
System Programming
"System-Numbering Plan (5/11)",
Call Waiting Set
Call Waiting Cancel
Conditions
Use the PDN button to assign and cancel Call
Waiting.
While Call Waiting is active, the waiting tone and
the display, if provided, are executed by the
following timing :
Call waiting tone:
15.0 sec
LCD display:
The new caller is The current other
shown flashed party is shown
5.0 sec 10.0 sec
Reference
VT Dumb
10-D-6.05 11-C-11.00
The new caller
is shown flashed
4-D-15
Call waiting tone can be assigned to two types by
specifying the timing according to the type of
arriving calls: calls from outside parties or calls
from extensions, as illustrated below :
Tone 1
15.0 sec
Tone 2
for calls from outside parties:
for calls from extensions:
5.0 sec
For selecting tone 1 or tone 2, refer to Section
13-C-6.00 "Call Waiting Tone Selection".