How to get cellular data network on iphone 4s?

I have just purchased my UNLOCKED iPhone4s through At&t, service works, i can call. But the thing is, i can't access cellular date network, my new carrier is Straigh talk. When i go to settings>general, i do not have the option "network". Why is that? I have restored my iphone 2 times. I have talked to At&t and Straight talk people and they were no help.

Return to apple