Part of the renewed appeal of Apple's [NASDAQ:AAPL] iPhone is the multitude of applications being written for its operating system. But like any hegemony, Apple hasn't given their developers free reign to write what they want. They've effected a kind of control by limiting the iPhone API, or application programming interface, which tells programmers the language in which their applications can communicate with the iPhone.
Now there's news that Apple has seeded their sundry developers with an API that will enable "push" notification in their applications. To iPhone owners, that means that applications that aren't currently running on your phone can still receive notifications. In other words, if you sign into AIM and then go back to the home screen and start up another application, you will still be notified if someone sends you an IM. Before, as with programs like Palringo (a chat client), you'd have to leave the app running to get messages -- and that meant either having it open, or returning to the home screen without opening another app.
Look for push notifications coming to applications near you by September.