I'm hearing impaired. I almost never use the phone part of my iPhone. But I use iMessage/SMS every day. And email. And twitter. And any other number of apps that bring me closer to the people I love.
Don't be so short-sighted.
Ok I apologize, however in context to the general population, this is still a salient point. More people text and email than phone or even meet in person. We're becoming too dependent on electronics for social connectivity.
One thing I wish Apple pushed through, back during the beta stages of OS X 10.5 there was a feature in iChat called "Answering Machine". This allowed users to leave an away video message and for people to leave one in return, it would have been perfect for the hearing impaired.
Leopard iChat Answering Machine