All over the world, apparently, being hacked and sold to work with GSM networks from Germany to Australia to China to Saudi Arabia, according to reseller Wireless Imports.
With a small orange device that you can buy for $179, Wireless Imports demonstrates in the following slides how to make your iPhone work on any GSM network -- even T-Mobile's here in the U.S. (although users should not upgrade their phones with Apple's 1.1.3 software update if they want this to work.)
First of all, users have to use Jailbreak to unlock their iPhones, which should take about five minutes, according to Wireless Imports.
Next, you get yourself one of these handy orange devices -- almost paper thin with a chip in the corner that somehow fools your iPhone into thinking it's working off an AT&T SIM card.