What carriers do with our data is a black box and changes all the time. They must do whatever the government compels of them. No opensource baseband options are available. Therefore I would not trust any of them.
It is best if you can decouple the phone number you use from the provider of the SIM card.
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Get a SIM card for data only with no KYC such as Mint Mobile or Ting for physical prepaid cards or jmp.chat or PGPP for pay as you go ESIM. Your voice and location give away your identity. So for maximum privacy, never make calls with the number associated with the SIM card nor activate cellular near your home.
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Transfer your number to a VOIP provider such as voip.ms or jmp.chat. Of course use encrypted messaging and calling as preference whenever you can.
For years I have been paying less than $20 a month and have a few phone numbers. Governments and corporations have no idea where I am. Because my phone is anonymous, they would have a hard time deploying malware onto it if they wanted to target me. Most data goes through a VPN.
Do they require KYC?