How to use your iPhone's portable Wi-Fi hotspot without a specific data plan?

I have 16gb iPhone 4S through AT&T and i want to know how to activate the portatble Wi-Fi hotspot. I have 2GB a month data plan for it. On my old phone a Galaxy S2 Skyrocket, i was not able to activate it because my data plan did not allow it. I then rooted my phone, and it worked just fine i was able to provide Wi-Fi to my laptop from my phone. When i try to turn it on, on my iPhone 4S, it says that my data plan does not allow this? Would i have to jailbreak it to use it? Or is there an app i can download to let me use it? Like i said in order to use it on my old phone i had to root it which is like jail breaking for android. I would prefer to download an app and not jailbreak my phone, but if i have to jail break it, how do i do it? Please and thank you?

Http://www.gadgetreview.com/2011/09/how-to-turn-your-iphone-into-a-wifi-hotspot.html