I pointed at the lack of source code as a starting point for proof of complete insecurity. I pointed at the ease of the existing protocols in active use as an example of that insecurity. That insecurity is the basis for Stingray fake towers. If you can fake the tower then the cellular modules can’t be much better.

I’m sure various agencies are quite frustrated by their inability to use the cellular modem as an entry point into Apple’s phones. That by itself is another pointer.

I didn’t claim to have proof other than that.