A communication system comprising a calling-side mobile communication terminal, a called-side mobile communication terminal and a communication control system, the communication control system comprising: a first mobile communication switching device for controlling the communication of the calling-side mobile communication terminal; a second mobile communication switching device for controlling the communication of the called-side mobile communication terminal; and a subscriber information management device for managing location registration information of both the mobile communication terminals (600, 700), wherein routing information is acquired and a calling signal is transmitted to the called-side mobile communication terminal before a communication line between the calling-side mobile communication terminal and the called-side mobile communication terminal is set, wherein the first mobile communication switching device includes, call request signal receiving means for receiving, from the calling-side mobile communication terminal, a call request signal including calling/called number specifying information that specifies a calling number of the calling-side mobile communication terminal and a called number of the called-side mobile communication terminal, and call information that includes at least one of calling number information specifying the calling-side mobile communication terminal and call type information representing a type of a call from the calling-side mobile communication terminal, and acquisition request signal transmitting means for extracting the calling/called number specifying information and the call information from the call request signal received by the call request signal receiving means, for generating an acquisition request signal of routing information, which includes the calling/called number specifying information and the call information, and for transmitting the acquisition request signal of the routing information to the subscriber information management device, wherein the subscriber information management device includes, acquisition request signal receiving means for receiving the acquisition request signal of the routing information from the first mobile communication switching device, mobile communication switching device specifying means for extracting the calling/called number specifying information from the acquisition request signal of the routing information received by the acquisition request signal receiving means, and for specifying the second mobile communication switching device controlling the communication of the called-side mobile communication terminal with reference to the location registration information of the called-side mobile communication terminal specified by the calling/called number specifying information, and issuance request signal transmitting means for extracting the calling/called number specifying information and the call information from the acquisition request signal of the routing information received by the acquisition request signal receiving means, for generating an issuance request signal of a routing number, which includes the calling/called number specifying information and the call information, and for transmitting the issuance request signal of the routing number to the second mobile communication switching device specified by the mobile communication switching device specifying means, and wherein the second mobile communication switching device includes, issuance request signal receiving means for receiving the issuance request signal of the routing number from the subscriber information management device, calling signal transmitting means for transmitting the calling signal to the called-side mobile communication terminal based on the issuance request signal of the routing number received by the issuance request signal receiving means, call information notifying means for extracting the call information from the issuance request signal of the routing number received by the issuance request signal receiving means, and for transmitting the call information to the called-side mobile communication terminal when the calling signal transmitting means transmits the calling signal, wherein the called-side mobile communication terminal is configured to select based on the call information whether or not to switch from a mobile communication network in which the called-side mobile communication terminal is resident to another mobile communication network in which the calling-side mobile communication terminal is resident, and acquisition means for receiving a response signal transmitted from the called-side mobile communication terminal in response to the transmission of the calling signal from the calling signal transmitting means and for acquiring the routing number, wherein the call information in the call request signal received by the call request signal receiving means is the calling number information specifying the calling-side mobile communication terminal, and the calling number of the calling-side mobile communication terminal in the calling/called number specifying information is used as the call information.