Basically, a good way to never trust "it's okay, the data is anonymized" again is simply knowing what the "Hemisphere Program" is.

https://www.eff.org/cases/hemisphere

In short, the US government got access to number from, number to, datetime, length and sometimes location information for every call passing through AT&T's network from 1987 to today.

Then they ran an algorithm to de-anonymize every burner phone based on behavior. They did this because maybe some of those burners were used by drug dealers.