I believe the problem is many telemarketers use some random-dialing call center applications that only transfer the call to a live person if a human answers. Call center apps can deal with incoming faxes, and I would assume a TDD person would not wait in silence (to be honest I don't know how call managers deal with TDD/TTY.
When I was setting up my last call center on our Inter-Tel (now Mitel) Axxess system, the system engineer I was working with asked if we would be supporting TTD/TTY callers ... I told him we weren't but if it was something we planned to do in the future would it be possible? He said it was. I didn't really probe any further -- kinda wished I had -- but looking back in retrospect it probably would have been an add-on device to the system.
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