Sure, iOS 4 adds some of the features that you previously had to jailbreak your phone to enable, including support for multitasking and changing the home screen background. But if you want to install apps that aren’t available through the app store, jailbreaking is still the way to go. It’s also the only way to get enable multitasking on older iPhone and iPod touch models.
Fortunately, the Dev-Team has released a tool that will let you jailbreak an iPhone 3G, iPhone 3GS, or 2nd generation iPod touch running iOS 4. The only catch is your phone will need to have been jailbroken prior to upgrading from iPhone OS 3.1 to iOS 4.
If your device fits the bill, you can go ahead and grab the PwnageTool 4.01 to get started.