at least if we also had open sim, both hardware and software, we could, unlike know, be sure that even if the tower wanted they could not infect our device.
because even if not probable, as i guess many people have monitored the sim, it's possible that they have a function in the sim that try to infect the OS or try to take over the GPS to give info to the tower.
the lack of transparency open the door for many bad thing to happen.