Will my iPhone 3G SIM card work in my iPhone 4?

My iPhone 3G is AT&T and the iPhone 4 I just got is Verizon. However, the iPhone 4 doesn't have a SIM card slot. Will it be able to work? If so, how can I do it? Can I do it by myself or do I need to go to the Apple store?

If there I not aim slot if could be a ipod or a fake but to be sure ask the person or company who sold it to you