[1] It works like this: Their "telephone" is an IP device with a camera that connects to their TV. When they make a phone call, they do sign language into the camera. This gets routed to a call center with a sign language interpreter, who makes a voice call to the person that the caller is trying to talk to. When the hearing person replies, the audio goes back to the call center, where the interpreter does sign language into a camera in their cubicle. That sign language displays on the deaf person's TV.

Scammers like this arrangement. At least one interpreting company (VRS) had to fight with the FCC about whether their interpreters could let the deaf person know that the call was a scam. The FCC's position was that this was supposed to be a faithful translation of the communication. But that was very hard on the interpreters, who were watching this person get scammed, helping this person get scammed, and couldn't do anything about it. Eventually the FCC relented, and now the interpreters can let the deaf person know it's a scam call.