This happened to me after getting my iPhone 4S that was activated for me about a week before I got it (I did NOT like the fact it was started up without me!). Once it tried connecting it to wifi, it did not let me no matter how many times I typed the correct code. Finally, I just SNAPPED and factory restet the whole new phone witout need of a backup. I'd recomend you do the same. If you did important things on your phone, you can always make a backup and restore your phone from that; I dont think a backup makes a difference. *Just so you know, the sooner this is done, the less time it will take in the backup process. Good luck!
Thank you for choosing Apple.