A long long time ago I posted looking for a solution to having TDD/TTY (Telecommunication Devices for the Deaf/Teletype machines). We did end up going with Textnet, which treats TDD/TTY calls as chats and routes them to agents logged into PC applications. It works well. The setup is simple, their support is good, and so far we've had no complaints about callers having difficulties with it. They have a long way to go on reporting, that would be my main problem with it, but a regular TDD didn't give me any at all either so I can't complain much.

So I'd definitely recommend it over a standard TDD/TYY hard wired into a phone line, but don't expect switch-like reporting.