From what I can tell, it's a replacement for the current SMS/MMS app on iPhones (and new on iPad, sans SMS/MMSing). People you text messaged before can now be i

From what I can tell, it's a replacement for the current SMS/MMS app on iPhones (and new on iPad, sans SMS/MMSing). People you text messaged before can now be iMessaged instead for free. People with non-iOS phones can still be SMSed as usual. So it looks like the end effect for users is that they use less text messages the more iOS-using friends they have. I guess if the network effect kicks in and everyone in your social circle ends up with an iPhones/iPad, messaging each other will be completely free - no need for text message plans anymore.