Apple has published a new support document outlining how the new Push Notification system in iPhone OS 3.0 operates. The article states that users must open any app at least once before it can receive notifications, and when restoring from a backup, the app(s) will need to be reopened to get notifications.
Notably, the article also states that when an iPod touch unit is on and has a Wi-Fi connection, notifications can be received at any time, but if the screen of the iPod touch is asleep, the device will check for notifications once every 15 minutes. It is unclear whether the iPhone, iPhone 3G, and iPhone 3GS exhibit similar behavior due to their persistent cellular connections.
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