See also:

Voice Recognition
The voice recognition system uses commands to control the system and dial phone numbers. Noise: The system may not recognize voice commands if there is too much background noise. When to Speak: ...

Capacities and Specifications
Engine Specifications ...

Customer Assistance for Text Telephone (TTY) Users (U.S. and Canada)
To assist customers who are deaf, hard of hearing, or speech impaired and who use Text Telephones (TTYs), GMC has TTY equipment available at its Customer Assistance Center. Any TTY user can communicat ...