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title: TTY Services | Relay SD
description: Explore the history and evolution of TTYs, which allow deaf and hard-of-hearing individuals to communicate over the phone using text-based messages.
---

 

![TTY Services](https://relaysd.com/hubfs/RelaySD_June_2022/Images/18_SDRelay_HeaderImages_collage3__1_.jpg)

 

# TTY Services

## Text Telephone Services using a TTY

Dial 7-1-1 or 800-877-1113

A person who is deaf, hard-of-hearing, or deaf-blind uses a TTY to type his/her conversation to a Communications Assistant (CA), who then reads the typed conversation to a hearing person. The CA relays the hearing person's spoken words by typing them back to the TTY user.

 

![Diagram TTY](https://relaysd.com/hs-fs/hubfs/RelaySD_June_2022/Images/Diagram_TTY.png?width=405&name=Diagram_TTY.png)

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### How it works