None of it matters. If the device has a SIM card (virtual or physical), it will execute commands sent over the network. It's required by the GSM/LTE standards. The best you can hope for is to have separate SoC for the OS and separate SoC for the GSM/LTE connectivity, but that means double the power consumption.

See presentation at DEFCON21 about SIM cards: https://www.youtube.com/watch?v=31D94QOo2gY

defcon21 is from the pre-snowden world (2013), for anyone else wondering. Mobile landscape (our reliance on them, the central role they play in our lives) back then was a little bit different and indeed I'd not be surprised if most models support that the carrier can remotely read out any memory location or something