IPhone 4 or 4s don't know which one it is?

So i recently bought an iPhone 4 at least thats what it said on ebay and what it says on the box. I consider myself pretty informed on apple products and know the only visible difference from the 4 and 4s is a little black line above the mute button. The phone i received has that line and i bought a screen for a 4 don't know if i should cancel the order or expect it to fit because the box says 4.

There's no visible difference between an iPhone 4 and 4s. The differences are the camera pixels, the screen resolution, the data speed, and the addition of siri.

The black line is attenna, and it varies from carrier to carrier.
its a 4s if it has siri without being jailbroke