I get kind of sad sometimes, watching people disappear into their mobile distraction devices. iPhones and their like certainly offer new opportunities for community and entertainment, but mostly it seems to me that they lead to isolation in one's physical context (aka, the real world) and lack of introspection.
So here is my idea for a truly useful iPhone app: Basta! (which means "Enough!" in Spanish)
Basta would allow you to request disabling of specific features of your iPhone (or all of it, just turn it into a black slate) for a given period of time.
Basta makes it easy for you to answer questions like: "Can I go 10 seconds without reading/writing texts?"
But the really exciting, Web 2.0 feature of Basta is that your friends (via Facebook, etc.) can challenge you to specific Basta restrictions: "I bet Steven can't go more than an hour without sending a tweet." and so on. All dares - proposed, accepted, denied and the results - are posted to your Facebook page and can be seen by others.
So you can build reputation and status around your ability, willingness, discipline to step away from devices and instead interact more with real live, breathing humans.
Or just watch more TV.
Anyway, that's my idea of a really great app!