Dear everyone suffering from RTT-
Google support is USELESS and has locked all threads on RTT. Samsung support does not even know the menus in their phones.
Apparently, via this thread and other forums, if your caller has RTT on, you get it automatically (unconfirmed).
My Galaxy S10+ has NO off switch for RTT. The default dialer via Verizon/Samsung took a UI dive recently.
I installed the Google dialer and the UI was better, but RTT was on EVERY call.
I had to get RID of it, and finally, I found
ACR Phone Dialer in the Google Play Store:
Highly recommend.
-Christian