There is a need for providing a content to a user in process of a voice call without interrupting the conversation. A presence server is provided to manage positions, in a virtual space, of a user of each of voice telecommunication terminals and an advertisement sound source provided by an advertisement server. A media server applies a stereophonic process to voice data for each of the other voice telecommunication terminals correspondingly to a relative position between a user of each of the other voice telecommunication terminals and a user of the relevant voice telecommunication terminal. Further, the media server applies a stereophonic process to acoustic data for the advertisement sound source correspondingly to a relative position between the advertisement sound source and a user of the relevant voice telecommunication terminal. In this manner, stereophonically processed data is synthesized to generate voice call data for the relevant voice telecommunication terminal.