Pod2g, the hacker behind the iOS 5.0 and iOS 5.0.1 untethered jailbreaks, has revealed that a public jailbreak for A5+ iOS 5.1 devices is at minimum weeks away.
Pod2g has asked the jailbreak community to send him any iOS 5.1 crash reports that are reproducible to assist in finding a jailbreak for the new firmware version.
Instructions on how to jailbreak and unlock your iPhone 3G on the iOS 4.2.1 firmware using RedSn0w for Mac. This tutorial can update your baseband if needed for unlock.
The iPhone Dev-Team has announced RedSn0w 0.9.15b1 which brings numerous new features including the ability to restore to older firmware not being signed by Apple.