this is quite interesting - I saw a letter in the Cerebra Bulletin (autumn 09) about communication aids, it was a Mum talking about how bulky her child's communication aid is, and that she had discovered an application for an i-touch/phone that can be used as a lightweight portable communication aid.
It was in the letters page at the back, I know so little about these things, but thought it might be of use/interest to people on here with dc who are non verbal. I can't link to it because I can't find the page yet.
The app is called Proloquo2go.