now someone just needs to make a simple, free iphone app that works just like the text messaging app, but sends messages through push notifications. no signup, no aim accounts, no presence, no other fluff.

send to any phone number or contact and the app would know if the receiving number is an iphone with the same app installed. if it isn't, it lets you know that you need to use regular text messages instead. resist the urge to implement real sms functionality on the backend so users don't feel like you're trying to sell them something. make the users pressure their friends into installing the app and it'll be huge. resist trying to make it some global contact manager with a desktop version and a dozen points of integration.

then make blackberry and android versions that can all work together and you're golden.