The present invention provides a caller with an arbitrary sound chosen by a called subscriber instead of a conventional RBT (RingBack Tone) without fails even in a flexible paging mode. In the present method: both exchangers check individually whether first information on replacing RBT or not and second information informing a route to a sound providing means have been stored for a called terminal, when an originating exchanger requests a trunk connection to said both exchangers according to a flexible paging procedure, and receive the first and the second information from a home location register after requesting if said information has not been stored, and request individually a trunk connection to the sound providing means while furnishing information identifying the called, based on the already-stored or the received first and the second information; and the originating exchanger selects one of the two paths connected to said both exchangers, and delivers to a caller an RBT replacing sound determined by the sound providing means that is received through the selected path.