Going a bit further, I would think there would be a market for porting “speech to text” software (like Dragon) into a mobile phone. You could even connect it to Google Glass to provide a “heads up display” so the hard-of-hearing person could look at the person being talked to, and see the text of what the person is saying.
“speech to text” software (like Dragon) into a mobile phone.”
Not being an expert in the subject, but as a former medical technician I can suggest that there is some forms of that available already. However, many deaf have difficulty with speech. How would you have learned to make articulate sounding speech if you never heard the sounds to begin with? Very challenging I’m sure.