Is this even possible on an iPhone?
My memory may be failing me or confusing things so please correct me, but I seem to recall reading somewhere that the baseband lives segregated (with only a narrow communication cannel, kinda as if it were a remote machine) from the remainder of the hardware, so while it could be made to run stuff itself it has no way to physically access to main cpu, ram, mic, nor cams (barring, of course, any vulnerability on the comm channel that would land an exploit in the main OS+hardware).
GPS is another matter, but then again it's baseband so it gotta communicates with towers, so that's a done deal already that does not even require baseband access.