Untethered jailbreak for iOS 6.x
As of March 19, 2013
If your device currently has a tethered jailbreak on iOS 6.0, 6.0.1, 6.1, or 6.1.2: you can install the package evasi0n 6.0-6.1.2 Untether to untether it.
If your device is not jailbroken on iOS 6.0, 6.0.1, 6.0.2, 6.1, 6.1.1, or 6.1.2: You can use evasi0n to jailbreak it untethered.
If you want to upgrade your device from an earlier iOS version:
Apple has released iOS 6.1.3, which means that any attempt to downgrade/upgrade/restore to an earlier iOS version with iTunes will fail with an error message. You cannot downgrade/upgrade/restore to earlier iOS versions using SHSH blobs on newer devices. Older devices that can use 6.x SHSH blobs are iPhone 4, iPhone 3GS, and iPod touch 4th gen.