For those who just can't wait until the iPhone SDK and third-party apps arrive next month, an iPhone 1.1.3 "upgrade" jailbreak has been released. It's Windows-only for now, and it requires that users upgrade from a 1.1.1 or 1.1.2 iPhone that has already been jailbroken. In other words: if you've already upgraded to 1.1.3 for all those shiny new features, you have a little downgrading work ahead of you before you can step up to a jailbroken 1.1.3 iPhone.

The iBrickr Windows app (great name, I know) hails from Nate True at cre.ations.net, and it works by guiding you through a process of downloading a modified version of the official iPhone 1.1.3 firmware. iBrickr then moves a packaged firmware installer onto the iPhone, after which you simply run the installer, wait around 15 minutes, and enjoy the shiny official features and all your extra third-party apps.

For those who don't have access to a Windows machine to do this with, True says to expect a Mac app soon. Of course, you can also just wait for Apple to officially launch an SDK and third-party app support.

Update: There is now a quick & dirty Mac OS X jailbreak available.