Good luck trying to do that. Your average mobile phone is running heaps of undocumented proprietary firmware in parts of the hardware/SoC that typically have full access to the whole device - there are no meaningful security boundaries whatsoever in most of those devices. If you are minimally security-conscious or your security model involves possible exposure to even mildly sophisticated attacks, you should treat your mobile phone as a toy. The attack surface is just too large for making them even minimally reliable to be a serious possibility. Even if you fix one part of the problem (such as the SS7 network the article mentions) that doesn't address everything else that's still raising serious issues.