Can I Use My AT&T Iphone on Straighttalk?

I'm buying an Iphone from my friend who uses AT&T services. I heard that I could activate this phone on the straighttalk network… I've already visited the site, and from my understanding, I'd have to purchase a Sim card and then one of the Plans from straighttalk… Does anyone know anything about this? Please Help!

Added (1). BTW, the phone is brand new and never been used!

Yes, I literally just did this to my iPhone but with net10. First you must get your iPhone unlocked and put your simcard in. Then you go and pay for your plan and call and get everything activated. It takes about 3 hours. A good site to unlock your iPhone with would be jailbreakunlock.info