Change RTT settings for accessibility on Mac
On your Mac, use RTT settings to set up your Mac to make and receive Real-Time Text (RTT) calls.
To change these settings, choose Apple menu 
in the sidebar, then click RTT on the right. (You may need to scroll down.)
Note: These settings are shown only when you have set up your iPhone and Mac for Wi-Fi calling and RTT phone calls are enabled on your iPhone. Wi-Fi calling and RTT are not available in all countries or regions or supported by all network providers.
Option | Description |
|---|---|
Enable RTT | Make and receive RTT calls on your Mac without using a special device. When this option is turned on and you make a phone call on your Mac, you can choose to use audio, RTT or RTT relay for the call. |
Send immediately | Send characters as you type them. To type full messages before you send them, turn this option off. |
RTT relay number | The relay service to use when you make an RTT relay call on your Mac. If a number isn’t specified, your carrier’s default relay service is used. |
After you set up RTT on your Mac, 
appears in some apps. For example, appears in Contacts when you move the pointer over a contact’s phone number to indicate that you can make an RTT call.
Depending on your network environment, an RTT call may be downgraded to a textphone call.
Important: When making an emergency call in the US on your Mac, special characters or tones are sent to alert the operator. The operator’s ability to receive or respond to these tones can vary depending on your location. Apple doesn’t guarantee the operator will be able to receive or respond to an RTT call.