Does Apple support RTT?

I am hearing impaired, but I can enjoy TV. I can understand much of the (audible) dialog, but some is not clear to me. But, with Closed Captioning (CC) I can glance down at the on-screen text to get more information.

I think that something like that might available for telephone conversation. I have read about Real Time Text (RTT). That sounds like it could augment voice calls.

I believe that that capability might be already included in computers. I found an Apple web page that seemed to say that that was possible, but I lost the URL and can’t find it again. One thing I remember was that an “apple modem tool” might be needed - but I can’t find that (Device ?, Software ?) again anywhere.

I would like to be able to use my Mac (Mac Pro) for RTT, if possible. I’d appreciate any light you could shed on this issue.

Glenn Haste