As promised below are the download links for all the iDevices, that support iOS 4. Along with the beta of iTunes 9.2 which is required to upgrade to the GM release (build 8A293). These have been tested and will work and I’ve read that you don’t need your UUID to be linked to a developer account for it to work. Also there is a jailbreak for the GM release.
Download iOS 4 GM (build 8A293) for iPhone 3G
Download iOS 4 GM (build 8A293) for iPhone 3GS
Download iOS 4 GM (build 8A293) for iPod Touch 2G
Download iOS 4 GM (build 8A293) for iPod Touch 3G
Download iTunes 9.2 Beta
If you want to jailbreak then:
Download Redsn0w 0.9.5b4-2
These are just the files that can be used however use at your own risk as by downloading the files you accept full responsibility for any damages caused. If your looking for a jailbreak guide then I won’t be posting one here just the files. If you search for a guide there are plently, just give Google a search.