Well, that's really the point, isn't it? If you can't think, you can't write. And vice versa, to some extent. If your writing is limited to what can be sent over a cell phone, you're never going to be able to handle anything very complex or deep. So these kids all need to learn standard English in school, and if teachers don't enforce, they're derelict in their duty.
But there have always been alternative dialects of English. We all use slang sometimes, right bro? In this regard, I don't find u-speak worse than any other dialect. In fact I think it's ingenious and kind of fun. (Not that I'm fluent in it -- I don't even have a cell phone.)
Some of the greatest writers in English have freely mixed the high and the low in their writing. Shakespeare and James Joyce, for instance. u know, like 2 b or not 2 b?