To enable a caller to originate a call to a callee while using a packet exchange network like Internet by exchanging network addresses, establishing a link between two telephone set interfaces through the packet exchange network and exchanging the audio data packets of audio signals between a caller telephone set and a callee telephone set.

In a typical speaking procedure, a call is originated through a public switched telephone network(PSTN) 12 to a call originating source or call originating side platform 14 while using an ordinary telephone set 10 by a call originating subscriber. The call originating side platform 14 responds to the originated call with a transaction number for specifying the caller himself or an application for asking a password code or the like and identifies the caller or call originating telephone set from the PSTN 12 while using an automatic number identification(ANI). The call originating side platform 14 inquires the telephone number of a person to be called to the caller as needed.