iOS 6 beta 3 can be jailbroken using the new redsn0w 0.9.13 dev 3 released by Dev Team

  During this night the Dev Team launched redsn0w 0.9.13 dev 3, a new version of the redsn0w program which jailbreaks for iOS 6 beta 3 that was released by Apple 12 hours ago. The new version of redsn0w has been specially modified to recognize ipsws for iOS beta 6 3, but no other changes have been implemented, so we are not talking about compatibility with other terminals or performing an untethered jailbreak. redsn0w 0.9.13 dev 3 does not install Cydia on your iDevices, so you will still have to use this tutorial.

  You can download redsn0w 0.9.13 dev 3 available here.