Panasonic KX-TDA600 Operating Manual page 197

Feature (While busy, DND or call tone is heard)
Call Waiting (BSS [Busy Station Signaling])
DND Override
1.3.3 Alternate Calling—Ring/Voice
1.3.4 Automatic Callback Busy (Camp-on)
1.3.7 Call Monitor
1.3.23 Executive Busy Override
1.3.42 Message Waiting
Feature (While dialing or talking)
Conference
1.3.20 Door Open
From any extension while talking to the doorphone
4.2 Feature Number Table
Default
1
6
5
3
4
Fixed
Number
3
5
Operating Manual 197