It appears iOS 5 has already been jailbroken and you can even install it now without a developer account, which costs money. First, go download the iOS 5 IPSW file. Then update your iPhone using typical iTunes method - connect your iPhone, click on the Check for Update button holding the Shift key on your PC or the Option on the Mac. Then you can select the iOS 5 IPSW file you downloaded. iOS 5 is still in beta, but it has 200+ new features, so you may want to be on the bleeding edge.
After you upgrade you have to activate it. Here's the hack from Gizmodo:
Activate iOS 5
1. Triple click the home button. This will activate the Voice Over.
2. Triple click the home button and Emergency Call will appear.
3. Click on Emergency Call and, while it's switching, swipe with your three fingers down.
4. The Notification Center will appear!
5. Click on the Weather widget. The Weather app will load.
6. Click on the home button to exit to the iPhone's springboard.
Now you can too enjoy some of the new tweaks and enhancements in iOS5. One of the biggest is Mobile Notifier, a completely revamped notification system for iOS devices that blows away the old notification system. Once you're running iOS 5, head over here for instructions on how to jailbreak it.
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