I’m way late in linking and sharing these:
If you want to find out what it’s like for a blind or partially-sighted person to use an iPhone, set it to Accessibility Mode: Settings -> General -> Accessibility -> VoiceOver On. There are options in that menu for Braille output devices and other assistive settings. You can set VoiceOver to toggle on and off with a triple click on the home button in Settings -> General -> Accessibility -> Accessibility Shortcut; which can be found at the bottom of the Accessibility page.
It’s interesting to experiment with alternative UI (User Interfaces) like this. Those settings are semi-hidden since most people will never need them, but they are essential for some. Since iOS 3 introduced VoiceOver APIs, Apple has steadily added all kinds of features for disabled users.
In addition to literally making the difference between independence and dependence for the people who use their software, some programmers have said that designing an app with usability in mind makes them concentrate on the details. That focus may actually result in better apps for people with unimpaired sight and mobility as well.