US Patent 7660398 Captioned telephone service

Captioned telephone are devices intended to provide text captions to persons needing assistance with telephone communications. Captioned telephones provide text by using the services of a relay interposed between the assisted user and the hearing user, the relay providing the captioning for the assisted user. While captioned telephone service can be delivered over a single telephone line, if the assisted user has two telephone lines available for the captioning service, additional features and advantages are possible in the delivery of captioned telephone service to the user.