iOS hacker MuscleNerd provided some very detailed insight about iPhone basebands and unlocks in a presentation at the Hack in the Box conference in Amsterdam today.
Since the first iPhone in 2007, the baseband that Apple uses for cellular communications has evolved in terms of both hardware and software. Some of the changes were minor but others were quite drastic and obviously aimed at deterring carrier unlocks. This paper details the most interesting of the changes and what effects they’ve had on both software-based unlocks and hardware-based SIM interposers. In addition to comparing the most recent baseband against its own earlier hardware and software incarnations, we compare it to other current Qualcomm handsets and discuss the ramifications of changes Apple has made to the traditional Qualcomm baseband boot sequence.
The complete slides can be downloaded by following this link.