Thanks to work by a hacker named Loktar_Sun, it is now possible to unlock a jailbroken iPhone with iOS developer Sam Bingner’s Subscriber Artificial Module (SAM)! This new unlock method works on the iPhone 4S as well as the iPhone 4, and only requires that the iPhone is jailbroken, as SAM is a package that must be installed in Cydia.
Full instructions for unlocking your iPhone using SAM can be found at this link. You’ll need to install SAM first by adding the following URL within Manage > Sources in Cydia:
SAM creator Sam Bingner has stated that he is currently developing a Cydia package in order to automate the whole unlocking process, although for now you’ll have to follow the slightly long list of instructions. The only downside of this exploit is that it requires that the unlock is performed individually with every SIM card, so you won’t be able to switch SIM cards while on the go without unlocking them every time you switch. Unfortunately, side effects like these sometimes come with unofficial unlocks that take advantage of exploits to get the job done.
On the bright side, in case Apple fixes this exploit in the future, the unlocks that have already taken place prior to that will remain valid, according to iPhone Dev Team member MuscleNerd who initially confirmed the legitimacy of the unlock.