TTY Support offers speech-to-text functions for the hearing impaired.
INSTRUCTIONS & INFO
Dial *983*889*1# to enter TTY full mode. Note: TTY requires a fully compatible TTY telephone. TTY Full mode will transmit and receive TTY characters.
Dial *983*889*2#  to enter VCO mode. Note: VCO mode will receive TTY characters but transmit by speaking into the microphone.
Dial *983*889*3# to enter HCO mode. Note: HCO mode will transmit TTY characters but receive by listening to the receiver.
Dial *983*889*0# to reset the phone to standard mode. Note: Standard mode will restore regular calling functions.