iOS4 cracked for 2G, 3G but bad news for 3GS
Apple released a new firmware upgrade, a MAJOR upgrade that is, the iOS 4 has been under the radar of Apple enthusiasts around the world and not only has it been released but its ready for cracking as well, phones running iOS 4 can now be jailbreaked with ease but of course there are certain restrictions.
Unlocking your iPod Touch 2G/iPhone 3G is a cake walk but unlocking your iPhone 3GS will involve it to be "Previously jailbreaked, make your own firmware and the possession of a MAC." So this a big WIN for the iPod Touch 2G/3G users but a big AWWW for the 3GS owners.
Of course the usual risks of jail breaking are still there, you can brick your iPhone, Apple gets angry and you automatically null your warranty if any. So you either jail break your iPhone at your own risk or you find someone to do it for you who is more experienced in this field.
For download links and further details head on over to the source
Source: Tom's Hardware