1. Dial *983*889*1# to enter TTY full mode (transmit and receive TTY characters).
   
2. Dial *983*889*2#  to enter VCO mode (receive TTY characters but transmit by speaking into the microphone).
   
3. Dial *983*889*3# to enter HCO mode (transmit TTY characters but receive by listening to the receiver).
   
4. Dial *983*889*0# to reset the phone to standard voice speaking and listening mode.