Panasonic KX-NCP500 User Manual page 49

PT/PS
outside line
Off-hook.
Seize outside line.
On-hook.
(If all required digits are stored.)
(ISDN Service)
OR
service code
(ISDN Service)
Press ISDN service.
Or press ISDN service and then enter service code and
then press ISDN service again.
(Requires to dial
additional digits.)
(ISDN Service)