My father (in his 80s) has very little vision left...basically one pretty blurry spot in his right eye. I didn't hear from him for a few days when his wife went into hospital because he couldn't see to dial the numbers.
Asking him what kind of phone would help him, he said that he's like a cordless phone with white numbers on black buttons, with the buttons large enough for him to make out (I'm guessing greater than 3/4"). It would be ideal if the dialing happened on the base station, but he was free to walk around with the handset.
Any suggestions?