Push notification has arrived on the iPhone, and in particular the AIM client. And I've used it for a day now, and it works perfectly, so far as I can tell. It's so good that it will make a perfect replacement for text messaging. On the iPhone, AIM is free, but text messages aren't.
Now, it's not perfect - everyone you talk to needs to have a mobile AIM client, or else they'll have to keep using text messages, and the coming ability to send multimedia messages wouldn't integrate with AIM the same way it would with text messaging. But for the most part, this ought to dramatically lessen our need for text messaging from now on.
Perhaps this will result in AT&T dropping the ridiculously draconian pricing scheme for text messaging. The value of it has certainly been dramatically reduced.