Panasonic KX-TDA6174 16-Port SLT Extension Card with Caller ID ECSLC1616-Port SLT Card with CID (ECLSC16)Supports Caller ID compatible single line telephones (SLTs)Includes 4 power failure circuitsRequires 1 free slotOnly installable on shelves that are equipped with a KX-TDA0103 L-type power supply..