Why are people talking about sim cards on here??!?! Most likely it has a bad ESN and cannot be activated. The most you can do is sell the phone on
eBay which you Gould get close to what you paid if you didn't over pay, or on
eBay their is a service for iPhones. For about $80 you send them your bad ESN phone and they will send you a clean one back. There are so many people getting screwed on Craigslist it's not funny. Sorry to hear you are one of them.