Full Story: http://www.ajc.com/business/content/business/stories/2007/08/24/IPhoneUnlocked_0824.html
According to the article, George took an AP reporter's T-Mobile SIM card, placed it into the iPhone and was able to place calls on the T-Mobile network. I think this kid is going to have a great career in the technology sector!
You can buy the phone or get more info on his blog: http://www.iphonejtag.blogspot.com/