George Hotz – well known to the iPhone scene as GeoHot – has put some efforts into analyzing the behaviour of the bootloader 5.8 that is running in many iPhone 3G’s. He found the signature checking of the bootloader is buggy. By exploiting this bug we are now able to up- and downgrade the bootloader. Sadly many of nowadays iPhone 3G’s contain bootloader 5.91. which added an RSA check that GeoHot could not circumvent yet. Read his whole article here.
By the way: this seems to be the same exploit the iPhone Dev Team used and released to be able to be used for manipulating (read our news here). Anyway GeoHot did standing work again. Kudos to you, dude.