IPhone 4 using old sim?

Hi, I had lost my iphone 4 recently and was given a new sim card for my old non smartphone. However someone had found my iphone 4, and I got it back. I was thinking, what if I can cut the sim card and put it inside the iphone 4.. I know at&t detects IMEIs, but is there any sort of hack/jailbreak tweak that can prevent at&t from recognizing this IMEI?

Btw my iphone isnt unlocked/jailbroken