Panasonic KX-TD500 - Manual (Page 270)

Features
270 Programming Guide
Parameter [Long Distance Call] Number to be added
Default 1
Value Range Up to 4 digits consisting of 0-9, or #
Description/Function Specifies the number to be added to the telephone number (sent
from the Central Office by Caller ID Service) to make up a
telephone number for long distance call. The number is added to
the beginning of the received digits.
Reference • 1.5 Attended Features (F/G)
– Caller ID Service