Apple has recently announced the new iOS 4 update for their devices including iPhone 3G, iPhone 3G S, iPod Touch 2G and other 3rd generation devices. This seems to be a major update in terms of features as it comes with over 17 new features
All the apple devices upto 3rd generation can update to this latest version of OS, but the some of the major like multitasking wont work on 3rd generation device including iPhone 3G due to old hardware.
Direct Download Links For iOS 4.0 Firmware Below
iOS 4.0 ipsw iPhone 3G here
iOS 4.0 ipsw iPhone 3GS here.
iOS 4.0 ipsw iPod 3G here.
iOS 4.0 ipsw iPod 2G here.