Here is an interesting article: https://theintercept.com/2020/09/25/surveillance-sim-cloning-protests-protect-phone/
I have 2 other suggestions:
- Leave your phone at home.
- Use an Apple iPod touch instead of a cell phone as it doesn’t have a SIM card and is nearly impossible to wire-tap or even detect by normal methods (see the previous article, The Most Secure Way to Communicate? An iPod Touch, at https://privacyblog.com/2015/08/20/the-most-secure-way-to-communicate-an-ipod-touch/. The primary drawback is that the iPod touch can only initiate or receive calls or text messages over wi-fi. There are several methods of carrying a wi-fi gateway with you although none of the methods I know of are convenient. Still, if privacy is important to you for business reasons, for political protests, or for any other reason, your needs might be worth the inconvenience.