Accessibility — also referred to as inclusivity — is all about making the iPhone, iPod touch, and iPad work for as wide a range of people as possible. That can include the very young, the very old, people brand new to computers and mobile devices, and also people with disabilities and special needs. With iOS, Apple has added features to specifically help those with visual impairments, including blindness, color blindness, and low vision, with auditory impairments including deafness in one or both ears, physical or motor skill impairments, including limited coordination or range of motion, and learning challenges, including autism and dyslexia. It also includes general features, like Siri and FaceTime which can provide significant value for the blind or the deaf. Many of these features can be found in Settings, all of them can be found on the iPhone and iPad.
Note: iOS 8 will be adding even more accessibility features for iPhone and iPad. Bookmark this page and check back later this fall when it's released!