Previously, three parties had demonstrated the jailbreak of iOS 5.1: I0n1c, the iPhone Dev-Team, and Chpwn/Phoenixdev.
The only claimed untethered jailbreak was by I0n1c; however, I0n1c has made it clear that he will not be releasing his jailbreak to the public.
Thankfully pod2g has announced that he's also succeeded in untethering the jailbreak.
Heya! My iPhone 4 running iOS 5.1 is now untethered :-)
Obviously, this is an important step towards public release of the iOS 5.1 jailbreak. This past Monday pod2g revealed the discovery of 2 big vulnerabilities. 1 kernel land and 1 root land. It appears that progress is being made!
You can follow iClarified on Twitter, Facebook, or RSS to be notified of any updates.