app, device, or user interface for communicating with hard of hearing person?

Problem: A person who has gradually lost his or her hearing over the years is unable to have a conversation with another person when the environment is too loud: e.g., many conversations are going on, or there is other background noise. The hard-of-hearing person is able to talk just fine; the issue is not being able to understand what the other person is saying. The hard of hearing person does not know or intend to use sign language.

Question: Given these circumstances, and assuming you have a mobile phone or tablet device with you, can you recommend the best way to communicate with this person?

Ideas: You could interact with the person by speaking into a mobile phone, and then the phone turns your speech to text, and you show the person your phone so they can read what you said. Issues that come to mind... Maybe an app already exists that does this well: i.e., that makes your speech to text verbiage large and legible - better than text messaging? I imagine the larger the screen for the hard-of-hearing person to read, the easier it is for them: tablet better than phone? Maybe there is a company that is trying to build a really "next level" interface: e.g., like one of those user interfaces you'd see out of a sci-fi movie, where digital information is projected into an otherwise empty area; that way, the hard of hearing person could read the text displayed near your head and you would not have to hand them your phone every time you say something. Maybe my assumptions are all wrong; maybe there is a better way to communicate than with a mobile device or tablet; thus, any insights with how to tackle this problem would be appreciated, especially if there is evidence for a particular approach based on the experiences of hard of hearing people.