Smartphones and tablets are evolutionary advances over their predecessors, but they are also more difficult for many disabled users to navigate. Android's basic accessibility features are pretty good, but they are focused mostly on visual impairment, and there are plenty of additional apps to meet the needs of users who have troubles with the basic interface or features. Here's a selection:
Users with visual impairment
The basics come preinstalled--but not enabled: TalkBack, KickBack and SoundBack offer nonvisual feedback. To get started with them, select "Settings," then "Accessibility," then "Enable Accessibility," then any or all of the three feedback options.
There's an easier way for most users, though. Download and install Apps4Android's Android Accessibility Installer for your phone by searching '"access 4" ideal' in the Android Market and selecting the package that is right for your carrier. This package will automatically install a broad range of apps, including Eyes-Free Shell, IDEAL Item Identifier, and the Rock Lock music player.
BIG Launcher is a great interface for folks who just need a little boost. It uses large, high-contrast icons to help guide users through their most common tasks.
If you want a little extra power, Sharon Vaknin just wrote up a great piece on how to get voice command on all your devices, including Android. Siri may not be available for Android, but there are still compelling alternatives.
Users with hearing impairment
While texting, Google Talk and other IM clients offer quite a few communication options for hearing-impaired users, and vibration can be used for practically any alerts, there are still a few gaps in the user experience. The somewhat unfortunately named Text to Speech Toy is great for those situations in which a hearing-impaired user needs to communicate face-to-face with someone who can't read sign language and either can't read or is otherwise difficult to reach through text. Of course, Google Translate is also a powerful tool for reaching out using sound, but it's much better for bridging language barriers.
You may also want to contact your carrier's customer service to see if you can arrange to drop your voice plan. Whole some hearing-impaired customers do use some voice time, for many, it's just a waste of money. Maybe your carrier can help you work something out--and the more pressure they get, the more likely they are to do so in the future.
Users with motor impairment
For users with fine motor impairment, BIG Launcher (mentioned above for folks with visual impairment) is a good deal. It uses larger icons and smart arrangements to make it much easier to start apps, make calls and more. For $1.39, it's not such a bad deal.Users who require more help to navigate their Android devices should consider Tecla Access. It is still a work in progress, but it aims to make Android devices (and all other major smartphones and tablets) accessible using the same equipment used to operate powered wheelchairs. For the time being, users will either need someone to put together an open-source Tecla Shield interface or wait for the commercial version to become available, but this could be revolutionary for many people, so keep checking back.