These phones can have closed captioning and several other easy systems for those who have a hard time hearing on the phone. Years before, most of my severe to profound hearing loss patients would have to have pagers and now with the advent of smart phones, it is much more helpful.  None of these smart phones are terribly loud though for your hearing.  The FCC rates most cell phones at a T2 or a T3 which is decent for amplification of sound.  We, at Hearing Solution Centers, have a phone which is not a smart phone but is powerful enough to a T5 rating to help with speech understanding.

A few Droid phones have more amplification than do the iPhone but I recommend that you listen to any phone before you take it home to see if it is powerful enough for you to hear upon.