This video shows the advanced capabilities of the iPad and the assistive technology available to it.
A company called AssistiveWare has already adapted for the iPad a communications application called "Proloquo2Go" it designed for the iPhone and the iPod Touch. "Prologuo2Go" uses symbols to represent phrases, or it allows users to type in what they want to say and the application then converts it to text-to-speech—giving users a voice they don't have.
Ideal for SEN students and specific learning difficulties e.g. dyslexia.
Unfortunately, the user disabled the embedding code, but here is the direct link to YouTube
Also, I thought it was worth mentioning that you can enable Windows 7 on an iPad if you wish to do so. See this video for more information: