The patch takes the iPhone up to 4.0.2 and the iPad to iOS 3.2.2 - but there’s no support for the original iPhone and iPod touch. This means that the only way to secure these devices against the exploit is to Jailbreak it. Is this Apple's subtle way of forcing people to upgrade?
Indeed, if you’ve rolled back your iPhone 3G due to its sluggishness with iOS4, you’ll also be left unprotected unless you Jailbreak.
For those who have taken the Jailbreak plunge, now would be a good time to update those firmware specific SHSH blobs, and if you haven’t already installed PDF Warner, there is a patch for the exploit on the Cydia store (called PDF Patch funnily enough), which means no one else can take advantage of it on your phone now that you have, so there's no need to press that upgrade button in iTunes.
Link: Apple support page