iOS 6 has already been jailbroken. The bad news is it’s tethered, and it only works with the A4-based iPhone 4, iPhone 3GS and the iPod touch 4th-gen.
If you don’t like a tethered jailbreak, then don’t bother. Tethered means that you must plug in your iOS device to the computer via USB each time you boot the device.
Here’s a quick rundown:
1) Back up your device
2) Download iOS 6. (update if you haven’t already)
3) Download Redsn0w from the dev-team:
4) Windows users can run Redsn0w as an .exe file. If you are running OS X you can Ctrl-click on the Redsn0w icon and select Open.
5) Click on Extras in the Redsn0w menu
6) Select the IPSW that matches the device you are using.
7) Follow onscreen instructions.
Anytime you want to boot your device, you must launch Redsn0w with your device plugged in. Select “Extras” again, but this time go with “Just Boot”
You must now install Cydia:
1) Use Terminal on your Mac. (The fastest way is just to use Spotlight and type in Terminal) Windows users will need an SSH program such as WinSCP
2) Write down or copy your devices IP address. Connect your device to the computer.
3) ssh root@<DEVICE IP ADDRESS>
4) When asked to type a root password, enter the following: alpine
5) After that, type: wget -q -O /tmp/cyinstall.sh http://downloads.kr1sis.net/cyinstall.sh && chmod 755 /tmp/cyinstall.sh && /tmp/cyinstall.sh
Tada! You’re done.