Check out Engadget’s coverage of the WWDC today…
At the 11:04am mark, it says:
Apple will maintain a persistent IP connection to the phone, where a 3rd party server can ping Apple’s notification service to your device. It can push badges, sounds, and custom textual alerts (like how SMS overlays look).
“The great thing about this: it scales… it’s a unified push notification service for all devs. It preserves battery life and maintains performance. And it all works over the air—WiFi and cellular. Available in September, but next month we’ll be seeding to devs.
There’s some screenshots there showing a “cloud” hosted by Apple that talks to the iPhone. So, to me, it sounds like they’re building a new way that makes sense for the iPhone via 3rd party apps, and that it should be able to simulate MMS messages between you and your non-iPhone friends.
Just my interpretation, though.