There’s a great article at MobiForge on how to set up iPhone Push Notification services.
This is Apple’s solution to the problem of not being able to run background applications. Unfortunately, it’s not a viable alternative for applications that need to monitor the phone state, for example, GPS. The push is from a server so for phone monitoring-type applications it’s only suitable for starting applications occasionally to see what’s happened. Even then, the user gets an Apple push notification message that the user has to’View’ every time before the application is started:
Hence, Apple’s push notification is only really useful for letting the user know about events that have happened on a server rather than on the phone.