This is the most disturbingly brilliant idea I've encountered in a while. R. and I are still trying to figure out why you need to pay to text when it's via wi-fi; I assume that's because it occupies the cellular network at some point in its journeys, whereas IM does not.
I'm not really a texter (okay, I don't text ever, except very occasionally in response to a text from B.); if I were, this would be tempting. And I'm _way_ outside the target audience.