Panasonic KX-TDA0190 Optional 3-Slot Base Card Equipped with 3 connectors to receive 1 or more of the following Optional Daughter cards: *4 Channel Message Card KX-TDA0191) (MSG4) *4 Port Doorphone/ Door Opener Card KX-TDA0161 (DPH4) *16 Port Echo Cancellation Card KX-TDA0166 (ECHO16) *4 Circuit Input/Output Card Contact Closure Card KX-TDA0164 (I/O)