Iphone 4 issues!@!

I had a jailbroken iphone 3g. while it was jailbroken I installed an ap that allowed me to change the carrier display name thats in the top left to what ever I wanted it to say. Since then apple has released IOS 4, so i went and purchased and Iphone 4. When i synced my iphone 4 to my itunes, the custom name that I had in the top left for my carrier transfered over, so my phone appears to be jail broken. How do I remove this? I ithought about resetting to factory defaults but I wouldnt be able to get all my contacts and pictures back with out re-syncing it...or would I? If you can help me out with any ides it would be great.

 

so when i restore and connect to my computer, and it asks if i want to restore from a previous back up i need to say no? im not sure exactly how to do to sync through address book though, is that an option somewhere?