Apple notified developers yesterday that Push notifications have been turned on and that iPhone developers can now start testing their applications with the service.
The Push Notification service is Apple's substitute for background processes and was originally planned for a September 2008 release. Apple announced in March that they would finally be delivering the service alongside iPhone 3.0 which is due this summer.Start testing your applications using the Apple Push Notification service today. Log in to the iPhone Dev Center and review the Apple Push Notification Programming Guide and Getting Started video
This system allows iPhone applications to receive updates while they are not actively running. Apple has claimed that allowing background processes on the current iPhone would sacrifice too much battery power for it to be practical.
Article Link: Apple Turns on Push Notification Services for Developer Testing