Panasonic KX-TD500 System Reference Manual page 369

Location of DN buttons is specific to each model as follows.
KX-T123220
MESSAGE
1
2
3
4
5
6
7
8
9
10
11
12
ICM
KX-T61620
CO1
CO2
CO3
CO4
CO5
CO6
ICM
MESSAGE
(Message
DN12
Waiting) Button
DN11
and Indicator
DN10
DN9
DN8
DN (Directory
DN7
Number) Buttons
DN6
and Indicators
DN5
DN4
DN3
DN2
DN1
ICM Button and
Indicator
DN6
DN5
DN4 DN (Directory
Number) Buttons
DN3
and Indicators
DN2
DN1
ICM Button and
Indicator
KX-T30820
CO1
CO2
CO3
ICM
4-A-3
DN3
DN (Directory
DN2
Number) Buttons
and Indicators
DN1
ICM Button and
Indicator