I have an iphone 4 which initially had ios5.1.1 installed on it. It was jailbroken and unlocked from 3 Hutchinson carrier. Recently, my cousin tried to update it to ios6 unaware about its jailbreak and unlock issues. Now i needed to activate it first before proceeding further. Using redsn0w i successfully performed a semi-tethered jailbreak on it. But my problem lies with unlocking for the baseband 04.12.02. On googling, i found out no unlock method is available for unlocking this baseband on ios6. Still, i ask if anyone has achieved success in unlocking, please provide me with a solution. Secondly, i tries to downgrade it to ios 5.1.1 using redsn0w. I had the shsh blobs on cydia. i stitched them to a custom firmware, put the phone in pwnDFU mode and tried to restore using iTunes. But it gave me a 1600 error. What should i do to get rid of this error. I have followed every tutorial/video for downgrading, but all in vain. Please help me out.