After a first iPhone that did not support third party apps, we were promised an App store, and push notifications for apps, in order to save battery life by not running applications in the background.
Then suddenly, we stopped hearing about it. Apple was acting like it never happened.
Now, with the iPhone OS 3.0 released, it is finally a reality. I strongly recommend that anyone interested in decent instant messaging on the iPhone get BeejiveIM 3.0 . It is about 10$, but worth every penny once you compare the security model with other applications, and push notifications make it so much more useful, it’s great.
With the iPhone locked, it will ring (if you want it to), and display the message you have just received in a small popup window. As you unlock it, it launches the app and takes you to that message.
Try it out !