iOS includes Universal Access, an additional set of features including screen magnification, a full-featured screen reader, reverse video, and more, that are specifically designed to provide accessibility to users with special needs.
Making Your App Accessible
Apple Human Interface Guidelines provide detailed instructions on how to create an intuitive interface that enables users with disabilities to accomplish tasks quickly and efficiently, while maintaining the consistency and ease of learning that characterizes successful iPhone applications. Developers that use standard controls and their subclasses will find that support for accessibility built-in. Apple’s Accessibility APIs define how iPhone applications can make their user interface available to an external assistive application or service.
Apple strongly encourages developers to support these APIs in all of their applications so they are compatible with features built into iOS such as VoiceOver, as well as other third-party products. The Xcode and Interface Builder tools, as well as the Cocoa frameworks, make it easy to add accessibility tags like roles and descriptions.  For example, Interface Builder has an Inspector that allows you to enter a description for any control in the user interface; that description will be synthesized to speech when VoiceOver is enabled.
How it Works
An assistive application interacts with accessibility objects in your application to allow people with disabilities to drive the user interface in non-traditional ways. For example, a VoiceOver user relies solely on an alternative set of gestures for control, and on Speech Synthesis for feedback. Users with low vision will view your application differently as well, using the built-in zoom and white-on-black display mode options to adapt the onscreen experience to their specific needs. Those who are deaf or hard of hearing will rely on vibration and visual alerts instead of audio.
If your application ignores the accessibility APIs, implements custom controls that have not been made accessible, or uses a non-standard gesture set, it may be inaccessible to a user who relies on Voiceover and other applications that use the Accessibility APIs in iOS. By following a few simple guidelines, you can insure that your application will work as intended for those who rely on these assistive features in iPhone.
With Universal Access and Accessibility APIs and technologies such as VoiceControl, Speech Synthesis, Voiceover, and a host of developer tools and utilities, iOS provides an extraordinary opportunity to deliver a superior mobile experience to every customer, including those with special needs.
