From a Home screen, tap Phone (lower-left).
If unavailable, swipe up on a Home screen to access all apps, then tap Phone.
Navigate: Menu (upper-right) > Settings > Accessibility.
Tap Real Time Text (RTT) Call to turn on .
If prompted with a 'No Video Calls or Call Merging' message, tap OK to accept. Then tap the Back icon (upper-left) several times to return to the calling screen.
With RTT enabled, from a Home screen, tap Phone (lower-left).
If not available, swipe up on a Home screen to access all apps,
then tap Phone.
Tap the Dialer tab (upper-left), enter a 10-digit number then tap the Call icon .
To place a call from the Contacts list, tap Contacts , tap the appropriate contact then tap the desired number to dial.