QUOTE(Berzerker @ Aug 22 2008, 08:37 PM)

You may be able to use it fine, but AT&T will complain and call you. They will suggest you change to the iPhone regular plan first, and if you don't do anything about it, they have the right to go ahead and change it themselves.
Was that directed at me? Enough people(on youtube and other forums) are using prepaid sims in their iPhones. So, I'm pretty confident it will work without any issues. I'm going to get the 3g, wait 30 days, cancel and then get a go phone. Since I'm already on At&t, hopefully, I can save $ on some of the start up fees. Through further research since I posted my initial question I'm sure that you activate the gophone first and then place the activated sim in the iphone.