But deaf people would still have the problem of not being able to hear.
Not to jump straight to crude jokes, but it applies. Everybody has problems. Yes, even if everyone could sign and every phone has a visual ring indicator and so on, people would still have the problem of not being able to hear. And some people would have the trouble of being an asshole (seriously not aimed at anyone, but the concept works so run with it). Deafness is a pretty small problem. Hell, I have combination skin (does anyone remember that commercial?), that’s a problem too.