Panasonic KX-TDA100 Features Manual page 217

[Example]
PBX-1
Interface
Extn.1011 Extn.1012
Dials "3011".
Explanation:
To use this method, it is necessary to change the first one or two digits of extension
numbers of either PBX (e.g., 10XX for PBX-1, 20XX for PBX-2) to avoid having the
same extension number.
Case 1:
Extension 1012 of PBX-1 dials extension number "2011".
Extension 1012 of PBX-1 is connected to extension "2011" of PBX-2.
Case 2:
Extension 1011 of PBX-1 dials extension number "3011".
Extension 1011 of PBX-1 is connected to extension "3011" of PBX-3.
b)
PBX Code Method (Access with PBX Code)
Dial the [TIE line access number] + [PBX Code] + [Extension Number].
[Example]
PBX-1
PBX Code 951
Extn.1011
Dials "7-953-1011".
PBX-2
TIE Line
Interface Interface
Extn. 2011
Dials "2011".
TIE Line
Interface
Extn.1012
Dials "7-952-1011".
[PBX code]
[TIE line
access no.]
[Extn. no.]
1.26 Networking Features
TIE Line
Interface
PBX-2
PBX Code 952
TIE Line
Interface Interface
Extn. 1011
PBX-3
Extn. 3011
PBX-3
PBX Code 953
Interface
Extn. 1011
Feature Guide 217