Cell phones for the signt-impaired

My aunt, who is in her nineties and slowly losing her sight, has decided that she needs to carry a cell phone. The problem is that (a) she needs one as simple as possible and (b) she can't read the display on most phones - the numbers are too small, and they use green or blue backlighting which doesn't help her eyes much.

Does anyone know of a phone that has a BIG display with numbers as large as possible, preferably doesn't do a lot of other things, will work on UK networks, and isn't ridiculously expensive?