Re: Trouble Down Grading to 6.0.2 from 6.0.3
He meant 6.1.3. And it's unlikely there will be a true jailbreak.
I'll explain the SHSH blobs quickly, as I'm guessing you don't have them. SHSH blobs are a snapshot of Apple's authorization to restore to that version of your iOS. In order to get these, you need to acquire them with your specific device while Apple is signing the iOS. If you don't know what they are, the only possible way you've acquired these blobs would have been to hit "make life easy for me" in Cydia on an older version of iOS while you were jailbroken prior to upgrading to 6.1.3. If you were jailbroken before, you can use redsn0w to query Cydia's servers to see if they saved your blobs for you. These would allow a downgrade using redsn0w.
Something you're welcome to try is the "semi-untether" that some iPhone4 users have had success with. To do that, acquire the 6.0 ((not 6.0.1, not 6.1.2, not 6.1)) IPSW for your phone. Be sure to get either CDMA or GSM depending on the phone you have. CDMA is Verizon or Spring. GSM is AT&T.
Download redsn0w from the dev-team blog.
In redsn0w, choose extras and select IPSW. Select the 6.0 IPSW we just discussed.
From there, select boot. Follow the on screen instructions and wait for your device to boot.
Go back to the first screen and choose Jailbreak. Ensure the "Install Cydia" box is chosen.
If it works, your phone will scroll some pretty little text while it's breaking. If it fails, your phone will be in DFU mode. Go back to the boot option and your phone will come back on.
Or, just wait until a more stable, easier method comes out.