StatusNotifier is an app that lets users see status bar notifications to their iPhones. There's a similar feature included in IntelliScreen, but if you don't fancy using that app just for the notifications feature, then this is perfect for you.
When it's installed, StatusNotifier adds an icon to the iPhone's status bar. You can see an example in the second screenshot above, the one with the arrow pointing to the upper right. It lets you quickly see if you have a missed call, voicemail, text message, or email.
StatusNotifier can be downloaded on Cydia for free. The app is currently at version 0.1.