Panasonic KX-TDA0161 ***REFURBISHED*** Optional 3-Slot Base Card - OPB3Good ConditionEquipped with 3 connectors to receive 4 Channel Message Card (MSG4), 4 Port Doorphone Card (DPH4), 4 Port External Input/Output Card (EIO4), or 16 Port Echo Cancellation Card (ECHO16)Mounts in optional card slot or ..