A system for operating a communication service, the system comprising: a transmission side terminal for requesting connection of the communication service, and for converting reception data or user input data, at the transmission side terminal, according to at least one of preset input/output modes and input/output modes determined by a user after the communication service is connected; a reception side terminal for receiving a communication service connection request from the transmission side terminal, for starting the communication service using the at least one of the preset input/output modes and the input/output modes determined by the user when the communication service connection acceptance request is accepted, for converting reception data and user input data or receiving converted data by transmitting the user input data to a speech process supporting device (400, 500) for converting the user input data according to the input/output modes, for outputting conversion data corresponding to the reception data, and for transmitting conversion data corresponding to the user input data; and a speech process supporting device for converting input speech data into text data and for outputting the converted text data or converting input text data into speech data to output the converted speech data, wherein at least one of the transmission side terminal and the reception side terminal is configured to: identify network evaluation information including at least one of a loss rate of a data packet and a transmission delay degree between the transmission side terminal and the reception side terminal, determine whether to operate at least one of Speech To Text, STT, service and Text To Speech, TTS, service based on the identified network evaluation information, and in response to determining to operate at least one of the STT service and the TTS service, operate at least one of the STT service and the TTS service. a transmission side terminal for requesting connection of the communication service, and for converting reception data or user input data, at the transmission side terminal, according to at least one of preset input/output modes and input/output modes determined by a user after the communication service is connected; a reception side terminal for receiving a communication service connection request from the transmission side terminal, for starting the communication service using the at least one of the preset input/output modes and the input/output modes determined by the user when the communication service connection acceptance request is accepted, for converting reception data and user input data or receiving converted data by transmitting the user input data to a speech process supporting device (400, 500) for converting the user input data according to the input/output modes, for outputting conversion data corresponding to the reception data, and for transmitting conversion data corresponding to the user input data; and a speech process supporting device for converting input speech data into text data and for outputting the converted text data or converting input text data into speech data to output the converted speech data, wherein at least one of the transmission side terminal and the reception side terminal is configured to: identify network evaluation information including at least one of a loss rate of a data packet and a transmission delay degree between the transmission side terminal and the reception side terminal, determine whether to operate at least one of Speech To Text, STT, service and Text To Speech, TTS, service based on the identified network evaluation information, and in response to determining to operate at least one of the STT service and the TTS service, operate at least one of the STT service and the TTS service. identify network evaluation information including at least one of a loss rate of a data packet and a transmission delay degree between the transmission side terminal and the reception side terminal, determine whether to operate at least one of Speech To Text, STT, service and Text To Speech, TTS, service based on the identified network evaluation information, and in response to determining to operate at least one of the STT service and the TTS service, operate at least one of the STT service and the TTS service.