[VoiceOps] Porting a TTY Line

Does anyone have any familiarity with TTY lines? A customer has asked us to port one, but I have no idea what, if anything is required on the back end. From the limited information I can find, it looks like a standard POTS line, but with a TTY terminal on both ends. But there's also the mention of an operator who acts like a go-between for communication. I'd like to know more about how it operates and what we have to provide / if we can provide it before going forward. Thanks Shawn