Tricky. Tricky. Call ATT and find out if you can, but the other posts are correct, the reason ATT stopped using the iPHONE in early July, is the elimnation of the unlimited data plan.
The iPHONE uses what is called a Server Depndent OS. Which means is requires updated from apple to funtion.Since gophone charges a .01/kb rate it is possible this trendy phone will drain your balance with data charges. Or even worse, you pul this off then the iPHNOE tries to update, then you get tha arrow on top, forcong you to activate through iTUNES. My verdict: Dont do it.