[deleted] Hey guys, I am thinking about this topic also for quite a while and I disagree with your statement here that you don't achieve anything by changing your SIM. It's true that the carrier connects the IMEI with the IMSI the first time you use the new SIM card because you register in the carriers network with your IMEI. But: It's way more complicated to track you based on your IMEI than with your IMSI. Not everyone inside the mobile phone network has access to your IMEI. Different service providers that are necessary are also located in different country's. You have one company that provides the cellular network towers, then you have the SIM card providers and you also have the roaming providers. Maybe there are even more but that are the ones I think about. The SIM card provider needs your IMEI to register your SIM and tie it to your phone but the roaming provider and the cellular tower providers don't need and don't have access to this information. Of course they could get this information from the SIM card providers but it's an extra step for them. So changing the SIM card at least changes the identity for 2 of the 3 providers I mentioned here.
Another thing to keep in mind is that it can be very good to protect your privacy if you use SIM cards that are issued in a different country that you are living in. Why? Because it's a lot harder for the network provider to get information about your identity if your card is not issued in your home country. For example: If you use a SIM card from Croatia and you live in the Netherlands, you can use this SIM like any other SIM from the Netherlands because you have free roaming. The mobile network provider in the Netherlands now just has your IMSI but because he has not issued the SIM, he does not know your identity and don't know your IMEI. Also the roaming provider does not know it. They would need to do a lot more work to get your name and any other personal information.
So to summarize this: Of course it's still possible to crack down on you, depending on your threat modle and what you do. If you are Snowden or Assange, that would not protect you because all the providers need to comply with the law and there are many ways to identify you, but if you just want to protect your data from analysis through 3rd parties and big tech, it can give you some better protection and it get's a lot more difficult to get all the data tied to your identity.
Additional steps that can help: Try to avoid SMS and the cellular network for phone calls. Use e2e encrypted messenger for your chats and phone calls as often as possible. Try to hide your network data by using a VPN and TOR in a good combination. Think about buying a VoIP phone number to do the calls and SMS that can't happen anywhere else. Because of that, it's harder for people who try to do a man in the middle attack with IMSI catchers to sniff on your SMS and phone calls because you use a network connection. Also then, none of the mobile providers can sniff on this data now (still you have the VoIP provider who can store data but it's harder for any other service provider to get access to the data). An additional benefit of that is that you can use your flight mode more often and convenient when connected to Wifi because you will still receive phone calls.
For everyone who struggles to get a physical no KYC SIM I would recommend look into silent link. They offer a great service for anonymous eSIMs that can be bought with Bitcoin and Monero. No additional information required. Keep in mind that in most country's where you are forced to do KYC when activating a SIM, it's still legal to buy and use a SIM that is already activated.
I would recommend this videos for anyone who is interested on that topic:
https://www.youtube.com/watch?v=tUVS-1_hUBM (Seth for privacy and Silent Link)
https://www.youtube.com/watch?v=Wh2tQOlMQiY (Matt Odell from Citadel Dispatch and Silent Link)
https://www.youtube.com/watch?v=dpDl887w4KA (Rob Braxman Tech)