The $50 card - available by mail order - is a serious piece of hacking, sorry, mobile phone coding, kit.
You apparently need a superSIM, a SIM reader/writer card with a USB connector to your PC, a copy of the Silvercard software and several files to copy to the iPhone.
Full details of the crack have been posted by Sassha, a Croatian hacker, who has published a guide in Hackin0sh, a rapidly growing Internet forum for peeps who want an iPhone, but don't want to use AT&T Cingular airtime.
Once unlocked, all the features of the iPhone reportedly work a treat, except that the YouTube facility doesn't operate for some reason.
Hey, I can live with that...