FakeCarrier is not an out of the world app but can be used for a change, to have your own name on your phone or some silly phrase or anything else you want. FakeCarrier, as the name suggests, allows user to change the name of the carrier service like At&T, Vodafone etc. You can use this app if you are using firmware 3.0 or later. With FakeCarrier you can also fake the time and the battery level of your iPhone.
After installing FakeCarrier you will see an icon on SpringBoard. Open Carrier >> Fake Carrier >> Enter desired text. Tap set and changes will occur instantly. Same steps can be followed to show battery level and time.
Below is the demo video of FakeCarrier:
FakeCarrier is available on Cydia via BigBoss repo for free. Here is another similar app jailbreak app for faking about screen