Especially since the mobile phone part legally can never be owned or controlled by the human person. Only corporations can own and use the baseband computer/modem because only they have bought the spectrum license rights and built out the infrastructure to justify it to the FCC. Similar situations exist in other countries.

This legal reality is showing itself more and more in the practicalities of actual using "smartphones". The only real solution is what op said, make the modem completely separate from the computing device.