That impossibility was due to the upgraded 4.11.08 baseband. But apparently an unknown China-based hackers called ‘VOLD’ has discovered a way to overcome the baseband blockade.
Again, that unlock is achieved through a SIM interposer (similar to the old Gevey), that acts by changing the IMSI (International Mobile Subscriber Identity) of your sim card, making the iPhone believe it is actually unlocked. The IMSI is an unique number with the country code, the Mobile Network Code, and the unique code to identify your SIM.
When the baseband is being loaded to the iPhone memory, those codes are checked and the iPhone is activated (in case the iPhone is unlocked to that specific carrier). The SIM interposer, by exploiting the 112 emergency number, achieves a “forced” connection, and quickly finds an acceptable code to make your phone think it is factory unlocked.
The new SIM is called MIRACLE, designed and made in or by VOLD.
At this stage, none of the suppliers we know has the actual working product in hand, and they all mentioned that it is rumored to be out before December 2011, which is less than 3 weeks away. All of these are still rumors, and you should only take it seriously once we have an actual test unit in hand. Jus follow UnlockBoot and Be First With Unlocked 04.11.08 Baseband on iOS 5 firmware !