|Singing Fingers is an iPhone/iPod touch native app; it also runs well on iPad.|
I see this app as having a lot of potential in stimulating and reinforcing speech sounds, but I have to admit, I don't have a lot of artic/phonology/apraxia students historically or lately! So, experts (with access to an iOS device), give this app a try and please let us know what you think in the comments. I look forward to hearing how you might use this app, or why you might not.
Here's an article on Singing Fingers in the New York Times. Thank you to Lillie's iPad for making me aware of this app.