To All - What Mr. "I" has is much more serious (medically) than what I have. My type of tremor is not as serious as Parkinson's, either.
Most (all?) cell phones do account for the fact that many people do need "hearing assistance". They have a "hearing aid mode" (whatever that does) - and most hearing aids can make use of Bluetooth technology to work along with almost any cell phone. Point is - technology does, in some cases, acknowledge the fact that some number of users (albeit a minority) need "special assistance" built in.
(Like many (most?) males, started losing hi frequency sounds quite a while ago. While I've used hearing aids for a year - never had trouble hearing on any kind of phone - so never had need to make use of whatever there is available for cell phones for the "hearing impaired".)