Panasonic KXDT590 is a Convenient & User Friendly Expansion Module for enhanced professional use 48 DSS buttons, to be used in full flexibility,

e.g.:
Direct Station Selection
PreProgrammable One Touch Number dialing
Frequently used features
Busy Station Signalling
Direct connected to the KXDT543/KXDT546
Maximum of 4 DSS console per phone can be connected
Available in black and white