This is a very lite version of ds1's communication aid (there's a paid for version at £90 ish as well - that's still a bit lite but has more words). itunes.apple.com/gb/app/unity-core-lite/id580724982?mt=8&dm_i=FVG,1246G,4OTR04,3DKNR,1 (free)
itunes.apple.com/gb/app/unity-core/id580721036?mt=8&dm_i=FVG,1246G,4OTR04,3DKNR,1 (£94)
I've only had a quick look but it looks as if the free version gives access to up to 60 words, with the £95 version giving access to 222 (ds1's device gives access to over 6000 words but it's also 6 grand!). In the states they have a version more similar to his talker, so that might follow. Although it also says it includes 3000 icons (or import your own pictures) so I'm not quite sure how that ties in.
I'll write something about it on my blog later, but for us this system has worked so well. It's not categorical, and we have found that while ds1 pretty much refused to use all other apps we tried (which do tend to be categorical), this one he has just flown with. We now get 4 & 5 word sentences produced spontaneously. He comments all the time, and well it's just fab. The system is called LAMP if you want to look it up.
I'm going to get this myself to use when we go to places like the beach I think, where I do get nervous about his talker being dropped in a rock pool.