The latest iPhone OS 3.1.3 update doesn’t really give you any significant benefit, unless you need the improved accuracy of the reported battery level. Of course, if you did install the update, and still want to jailbreak your iPhone, you’ll be happy to know that the Dev-Team has already come up with a new version of the PwnageTool (v3.1.5 for Mac), which is compatible with the latest iPhone OS. It gets better, as the tool even preserves your iPhone’s ultrasn0w unlock and jailbroken state. As with any Jailbreak news, we’d strongly suggest you to backup you data in case things go awry, and read all the juicy details from the Dev-Team before you attempt this.