The iOS 5 Notification Center displays incoming messages in a couple of ways. When you have an iOS device unlocked, a new message can be shown via a small banner notification at the top of the screen. A regular alert can be displayed for certain apps, and incoming notifications are also pushed to the iOS lock screen when a device is locked. The system works well, but Apple restricts the amount of text you can see in a given notification. If you want to read an entire message that’s more than a sentence or two, you have to open the associated app.
The jailbreak community has improved the way Notification Center handles longer messages. A new Cydia tweak called Reveal lets you view long chunks of text from a banner or lock screen notification.