Can I get service in a used iphone?

What happen is this. I find an iphone 1 month ago, it was from a tourist, so I never give it back. But I want to know if I can activate it, even knowing I don't buy it. It is verizon. More specific, change the number to a new number, new service, but with the same iphone. Can I? If not, what can I do?

Added (1). I forget, the iphone don't use SIM card

Yes of course!

If that person has claimed an insurance on that iphone then you can't use it for verizon, but if you can jailbreak it and unlock it with a gevy sim card then you can use it for any career, don't update it or anything if you don't know any thing about unlocking it or jailbreaking take to a cell phone store and tell them to unlock shoulldnt cost you a lot.