AASTRA 4223 Professional for BusinessPhone User Guide - Manual (Page 121)

121 BusinessPhone — Dialog 4223 Professional / Dialog 3213
Installation
Install key panels
1 Remove the small plastic plate, marked DSS, i.e. with a
screwdriver and connect the cable.
2 Attach key panel unit.
3 Secure with screws and install stand.
Note: All key panels must be of type DBY 419 01 (three or
four key panels can only be used in newer versions of the
exchange).