American Communication & Networks Corp. (ACNC) manufactures the popular and versatile DoorBell Fon. The DoorBell Fon replaces the traditional doorbell to let you answer the door from any telephone, even cordless phones. Also open the door with one simple keystroke (requires Electronic Doorstrike). Start with one of Doorbell Fon kits, and expand your system with extra doorboxes! The DoorBell Fon connects to 2 doorboxes and allows you to flash between the 2 doors.