We just told you that a first public beta jailbreak was released for iPhone OS 4.0. Again, if you are running on FW 3.x DO NOT update to 4.0 just because you got a jailbreaking tool available. Everything is really really really buggy, and not meant for average end-user. But if you do, you might as well enable multitasking on your iPhone 3G.
1. Jailbreak your iPhone, and install OpenSSH
2. SSH into your iPhone and browse to /System/Library/CoreServices/SpringBoard.app/N82AP.plist
3. Copy that N82AP.plist on your computer and edit it with any tool you like. I used TextWrangler. All you need to do is to add the following string and save the plist. Check screenshot below…
4. Now , copy the edited .plist file back into your iPhone over-writing the one in the phone. Since SBSettings is not working on OS 4.0 , you need to reboot the iPhone. That is it. Now double tap the home button , and woop… there it is.