Panasonic KX-TD500 System Reference Manual page 375

Location of DN buttons is specific to each model as follows.
KX-T123250
MESSAGE
1
2
3
4
5
6
7
8
9
10
11
12
ICM
KX-T61650
CO1
CO2
CO3
CO4
CO5
CO6
ICM
MESSAGE
(Message
DN12
Waiting) Button
DN11
and Indicator
DN10
DN9
DN8
DN (Directory
DN7
Number)
DN6
Buttons and
DN5
Indicators
DN4
DN3
DN2
DN1
ICM Button
and Indicator
DN6
DN5
DN4 DN (Directory
Number)
DN3
Buttons and
DN2
Indicators
DN1
ICM Button
and Indicator
KX-T30850
CO1
CO2
CO3
ICM
4-A-9
DN3
DN (Directory
DN2
Number) Buttons
and Indicators
DN1
ICM Button and
Indicator