18. A data processing apparatus according to claim 17, wherein said causing means includes means for causing said displaying means to display said first information such that said first information is indicated by every predetermined amount of data.
17. A data processing apparatus comprising: inputting means for inputting alphanumeric character data representing a message to be transmitted; storing means for storing the alphanumeric character data input by said inputting means; displaying means for displaying said alphanumeric character data stored in said storing means; and means for causing said displaying means to display first information indicating to a user, key operations of a push-button telephone corresponding to said alphanumeric character data stored in said storing means so as to input a message corresponding to said alphanumeric character data by the user performing said indicated key operations of said push-button telephone connected to a public telephone network means; and wherein said causing means includes converting means for converting said alphanumeric character data stored in said storing means into said first information indicating a series of key operations of the push-button telephone, based on a preset data conversion format.