Panasonic KX-TDE620 Expansion ShelfExpansion Shelf for the KX-TDE600 systemProvides an additional 11 slotsIncludes 1 BUS-S stacking cardMaximum of 3 can be installedRequires BUS-M KX-TDA6110 and BUS-ME KX-TDA6111 cards to be installed on the basic shelfPower supply not included..