3G and 3GS iPhones don't need to be unlocked to use a GoPhone sim in them. Just insert the sim and you are ready to go.
If you want data, it's 1MB for $4.99 or 100MB for $19.99. You would need a custom APN uploaded to the phone to use data since the phone blocks data on sim cards not on official iPhone plans.
Hi. I seem to be getting a lot of conflicting/ confusing info on the AT&T prepaid option. On the one hand, I read that it's as easy as plugging-in a gophone SIM and voilà. On the other hand, I'm being warned that AT&T would contact me and order me to stop using my iphone on a prepaid/ data plan... Now the latter sounds a bit far-fetched but, I suppose anything is possible.
What's the consensus here about this? Again, thanks for all your input.