There are other solutions... There are 😄

You got me interested

You got two key issues. They trace your phone by IMEI and cell positioning system. They can use GSM hardware commands to make your phone do things your do not like. Only way I see is totally detach internet connection from the phone using an external LTE with a VPN tunnel to a self hosted VPN server located where you like. Use a phone where the Bluetooth/wireless/GSM chip has been removed and connect by usb-c port to the tunneled LTE. If you get a simm card not in your name they should not be able to get any data or be able to get where your communication is redirected. For GSM voice we are experimenting about connecting to the network with an LTE dong and redirecting the line to your self hosted VOIP server. This way they cannot see where you are, who is the owner of any of those devices or force your phone to give position data. Ok.. not easy but very interesting and apart from the last it already works

Ok that’s valid if someone is planning terrorist attack or is smuggling 15t of cocaine and wants to be completely invisible in which case all this is jast waste of time and energy because you want to be completely off the grid and never use any electronic device. My use case is simpler - I just don’t want curious motherfuckers to read completely legal and harmless messages I send to my friends and family.

Well. I just want to protect my kids from government interference and being able to buy and hold assets around the world without them sneaking around my stuff. I have zero confidence about their motives. But yes I started this road more than 20 years ago so they do not have any information about me or any picture on Internet. . I do not sell weapons or print money or do bombs but if it will be necessary to survive I will be able to.