How do I know my iphone 4s is unlocked?

I've gotten an iphone 4s when it first came out on a 2-year AT&T contract. Now that the unlocked iphones are out, I bought an unlocked iphone 4s looking to use it with my locked iphone 4s' AT&T sim card. I took the AT&T sim card out, and put it into the unlocked iphone, and set things up, restore backup.

After everything's done, the iphone section in the iTunes looked exactly the same as my AT&T locked iPhone... there wasn't any "Congratulations, your iPhone has been unlocked" message or anything.... So, how do I know if my iphone is really an unlocked iphone or not?