Changing SIMs might be useless, since the carrier can track phones by their unique IMEI ( https://en.wikipedia.org/wiki/Imei https://en.wikipedia.org/wiki/Imei

Changing SIMs might be useless, since the carrier can track phones by their unique IMEI ( https://en.wikipedia.org/wiki/Imei https://en.wikipedia.org/wiki/Imei ) and when you use another SIM on the same phone to talk/chat to your friends, 'gov sigint' can use that information to get to you.