Gevey SIM is your next hope for iPhone 4 baseband unlock, The Gevey SIM functions as an interposer between the SIM card and the baseband hardware. Unlocking iPhone with Gevey SIM is easy as one, two, three. Simple install the Gevey SIM then call 112, once the call connects you hang up then toggle Airport mode on and off and that’s it.
Now darker side of the method, as we we mentioned earlier that unlocking procedure requires you to call 112, which is a legitimate emergency number and needless to mention that dialing the emergency number without any reason is punishable offense in some countries. Another glitch in this method, it could be rectified by a firmware update or carrier update.
For more technical detail on how Gevey SIM work, we recommend you to read an article over here
SIM card holds many different types of information, but the part most involved with carrier lock is the IMSI number, which is a unique code that corresponds to your account in the mobile carrier’s database.
When the iPhone baseband is loaded into memory, it checks the MCC and MNC against its own network lock state stored in the seczone. If the combination is allowed, the cell radio is activated and vice versa.
The earliest iPhone baseband revisions only check IMSI twice following a restart, therefore it is very easy to send spoof information in order to bypass the check. Nevertheless, the baseband was soon updated to validate SIM more aggressively and the method soon became obsolete.