The 3CX Phone System supports the use of door phones. Both audio and video door phone are supported, when combined with a video handset users can see who is at the door. Most door phones support DTMF strings. This enables the user to enter the string (for example 546) and the door would open. There are many reasons why integrating the door entry system with the telephone system benefits a business but here are a few. Maintenance cost reduced by using only one system; Call groups can be dialled so anyone can respond to visitors; interact into the existing computer network cabling.