Panasonic VB-44310 24 Button Expansion Unit:

Panasonics VB-44310 provides 24 programmable feature, line or Direct Station Selection (DSS) Busy Lamp Field (BLF) keys (dual colored LED). This unit is used in conjunction with a digital station. It comes equipped with a joining bracket to connect to the telephone giving the appearance of one complete unit. Requires one digital port. Wall mountable. Includes elevation supports