A Gold Master release of iOS 4 (née iPhone OS) was seeded to developers yesterday. And the next iPhone's software has been surprisingly accommodating to jailbreakers' attempts to crack it wide open.
The current technique was finagled from existing jailbreak software (Pwnagetool, specifically) by msft.guy. On top of this prerelease hack, the iPhone Dev Team is claiming to have an unlock of their own nearly prepped for iOS 4 final, to be released within a month (presumably to coincide with the release of iPhone 4). In other words, come iOS 4's official release, you should be able to jailbreak your handset—or at least your iPhone 3GS. (Nobody's been able to test the exploit on an iPhone 4.
gizmodo.com/5558277/ios-4-jail…