A couple of weeks ago, The Economist published an article on why texting hasn't taken off in the States. And I think it's wrong.
"The short answer is that, in America, talk is cheap ...Texting first took off in other parts of the world among cost-conscious teenagers who found that it was cheaper to text than to call, notes Jessica Sandin, an analyst at Baskerville. But in America, you might as well make a voice call."
I think that misses the point. Text messaging isn't a replacement for talking on the phone - it's another part of the spectrum of communication methods possible, perhaps sitting closer to email and voice mail, than the traditional synchronous phone call. The 'fire and forget' capability of the text message is its huge advantage, allowing sender and receiver to process the information when they see fit. This is entirely different.
That's not to say I for one don't have text 'conversations' which are as lengthy and rich as many voice calls, involving numerous calls and responses. However, the ability to multitask while texting is another huge advantage over the synchronous voice call.
The article makes more sense when saying that IM has taken off amongst American kids instead. Although, again, the mobile aspect of texting (which IM can't augment yet, with some notable bleeding edge exceptions) is a killer aspect. The main reason texting hasn't taken off in the States is surely, and simply, the lack of interoperability, which the article cites as a secondary influence.
Better summary of mobile usage (in the UK at least) here, though doesn't go into texting much.