Not a pro here and I’m pretty sure lots of folks here knows this case much better than I do but I still will try to help you on that matter. (but you should have posted your question on a dedicated thread like this one)
I don’t know if CSPs have got this kind of access but on most modern cellphones the broadband adapter is integrated so it does have access to memory.
On the Librem 5 the broadband adapter is physically separated from all of the other parts of the phone and has got only access to what the CPU gives it orders on what it has to do atm and nothing else.