Technology they are .. However it's the device that's locked and won't allow you to have service with just any sim. Some sim's do have proprietary locking on them aka "tracphone" ...
that's not true you can use a prepaid SIM on an iphone 3g/3gs that's locked. i'm currently using one in my 3g. i literally took my SIM and put it in the iPhone and it just worked.
you have to make sure you get a plan that does not advertise bonus airtime on the box because if it does, it locks that SIM to the phone you activated it for six months.
has nothing to do with the sims, has nothing to do with the phone, has everything to do w/ ATT & they do regular scans of the network, and can check the identity of the phone remotely. If they find your phone on a prepaid plan they can/will switch it to the post paid iphone plan.
I dunno where you're getting your facts from but people have been using iphones on prepaid plans without at&t automatically switching them to post paid for a long time.
Honestly, i think that whole thing is bs and is some kind of scare to prevent people from even trying to do prepaid iphones.
But taht is expensive. So the prepaid card would be a grrater choice. Could you somehow unblock those permissions or what they are which doesn't let you use prepaid cards?