There is already a hearing-impaired plan from AT&T for the iPhone, but now that the iPhone 3G has been released, the plan got a bit of an overhaul, at least in the price department. 
Prior to the 3G, the plan cost $40 a month. It included unlimited SMS and data transfer, and visual voicemail though phone calls were $.40/minute.
For the 3G, the plan has merely been raised $10--just like all of the other iPhone 3G plans. Not too bad when you get down to it, but for some the $10 difference can mean a lot.
[via iPhone Matters]
Hello: I would like to know how soon will it be ready for me. I did contact you last summer when it was released to new 3G iPhone and you said it would be ready this month. Please reply this. Thank You! (This is for hearing impaired situation.) (Overhaul should be ready this month.)