Teletype (TTY, also known as Telecommunication Device for the Deaf, or TDD) transmissions are moded. The same sequence of tones may code for a letter or for a figure. When a TTY device is transmitting to a text-based Internet Protocol display device, via a TTY-to-text conversion gateway, the text will not be displayed properly if the TTY device and gateway are out of mode synchronization. To fix the problem, either a signal received from the destination terminal causes the gateway to change its conversion mode from letter to figure or vice versa, or a signal input by the end user or automatically generated by the destination terminal causes the destination terminal to display the other character than the received letter or figure that is coded to the same TTY tone sequence.