When a line for communication of audio signals between first and second portable-telephone devices through a first portable-telephone base station, a second portable-telephone base station and a portable-telephone line network has been connected, IP addresses are exchanged. The IP addresses are required for communicating image data by first and second terminal adapters associated with the first and second portable-telephone devices respectively through an OCN. Image data is then transmitted to the IP addresses received in the communication through the OCN. To put it concretely, an image of the user of the first portable-telephone device is transmitted by the first terminal adapter through the OCN to the IP address of the second terminal adapter to be displayed by a second television receiver associated with the second terminal adapter. By the same token, an image of the user of the second portable-telephone device is transmitted by the second terminal adapter through the OCN to the IP address of the first terminal adapter to be displayed by a first television receiver associated with the first terminal adapter. Thus, by merely taking a portable-telephone device to a place like a store selling home electrical appliances including a television