If you look at the Fairfax County Emergency Phone Numbers, you will see tty 711 located near many of the listings.
Did you ever wonder about 711???
"If you have a speech disability or need to call someone with a speech disability, you can dial 711 and ask for Speech-to-Speech. Give the operator the name and number of the person you are calling and remind this specially trained operator to repate everything your caller says. This free government service is available 24/7 nationwide."
Additional information can be found at http://www.SpeechtoSpeech.org