Want to have a homescreen wallpaper on your iPhone 3G running iPhone OS 4.0? Here’s how:

1. Jailbreak your iPhone
2. Install OpenSSH via the Cydia app
3. SSH into your iPhone and browse to: /System/Library/CoreServices/SpringBoard.app/N82AP.plist
4. Copy that N82AP.plist on your computer and edit it
5. Copy the edited .plist file back into your iPhone over-writing the one in the phone.
6. Reboot your iPhone
7. To edit your homescreen open up the Settings app

And there you go! Your iPhone 3G now has a homescreen wallpaper!