Watch this video, fire up Cydia on your iPhone, add http://phajas.xen.prgmr.com/repo to the repositories and install „MobileNotifier“ NOW! It is even FREE!
EDIT: Keep in mind though, that this thing is still beta and some things still need fixing. Notifications aren’t shown on the locked Display anymore. You first need to either push the home button or the on/off switch to wake up the device in order to actually see the notification. If you have notifications that you didn’t read already, you won’t be able to see the time on the lock screen anymore. But I’m sure Peter Hajas will fix that soon… ish… ly… 🙂