An audio/video communication system is provided which includes: a web server providing a user system with a phone icon or button indicating a call receiver and transmitting a phone identifier LN for identifying the receiver allocated to the phone button when a user clicks the icon or button; and a gateway module performing a call setup in response to a data connection request for the audio/video communication from the user system, specifying the user identifier DN for identifying the user system from another user system, transmitting the phone identifier LN to the IP-based telephone exchanger, and relaying a communication between a phone connected to the IP-based telephone exchanger and the user system to progress the audio/video communication.