TTY users are declining. I don't know the statistics, but 80% of my interaction with the Deaf is by Videophone (VP) (aka video relay service (VRS)).
Training staff on how a VRS or TTY relay call works is pretty simple. A few general rules are:
1) Talk as if you are addressing the Deaf person directly (don't say, "tell her hello", say "hello").
2) Speak in discrete chunks of meaning with pauses in between to give the interpreter a chance to catch up.
3) Expect everything you say to be interpreted.
Training staff on how a VRS or TTY relay call works is pretty simple. A few general rules are: 1) Talk as if you are addressing the Deaf person directly (don't say, "tell her hello", say "hello"). 2) Speak in discrete chunks of meaning with pauses in between to give the interpreter a chance to catch up. 3) Expect everything you say to be interpreted.