A network information system, which comprises: - a stationary telephone terminal, a first portable telephone terminal, and a second portable telephone terminal, - a server (203, 208) comprising an emulation unit adapted to convert control data received via a communication line into operation control data for the corresponding application program, and - a signal converter (201, 206) comprising a signal-converting unit that is connected to the stationary telephone terminal, the first portable telephone terminal and the second portable telephone terminal via public communication lines and is configured to convert a DTMF signal from the stationary telephone terminal, the first portable telephone terminal and the second portable telephone terminal into predetermined control data, and a data-transmitting unit adapted to transmit the control data to the server via the communication line, wherein each of said stationary telephone terminal, said first portable telephone terminal, and said second portable telephone terminal comprises a keypad and is configured to transmit a DTMF signal to said signal converter in response to an operation of said keypad; the server (203, 208) further comprises a processor (31, 35) for executing an application program using said operation control data converted by said emulation unit, wherein said operation control data corresponds to one or more of said stationary telephone terminal, said first portable telephone terminal and said second portable telephone terminal; and the server (203, 208) further comprises a screen display (204, 209) for displaying a screen under the control of the processor executing the application program, characterized in that said server (203, 208) further comprises: a connection instructing unit for providing a connection instruction including a designation of at least two telephone terminals of said stationary telephone terminal, said first portable telephone terminal, or said second portable telephone terminal on the basis of an executed result of said application program, and transmitting said connection instruction to said signal converter (201, 206); and said signal converter (201, 206) further comprises a voice communication line forming unit for forming a voice communication line between said stationary telephone terminal, said first portable telephone terminal, or said second portable telephone terminal designated by said connection instruction. - a stationary telephone terminal, a first portable telephone terminal, and a second portable telephone terminal, - a server (203, 208) comprising an emulation unit adapted to convert control data received via a communication line into operation control data for the corresponding application program, and - a signal converter (201, 206) comprising a signal-converting unit that is connected to the stationary telephone terminal, the first portable telephone terminal and the second portable telephone terminal via public communication lines and is configured to convert a DTMF signal from the stationary telephone terminal, the first portable telephone terminal and the second portable telephone terminal into predetermined control data, and a data-transmitting unit adapted to transmit the control data to the server via the communication line, a connection instructing unit for providing a connection instruction including a designation of at least two telephone terminals of said stationary telephone terminal, said first portable telephone terminal, or said second portable telephone terminal on the basis of an executed result of said application program, and transmitting said connection instruction to said signal converter (201, 206); and said signal converter (201, 206) further comprises a voice communication line forming unit for forming a voice communication line between said stationary telephone terminal, said first portable telephone terminal, or said second portable telephone terminal designated by said connection instruction.