When you have the entire call graph, it's almost trivial to match it up to names. And then you know who everyone calls and who calls them, which I would argue is almost as fundamental an affront to privacy as knowing the actual content.
I suppose the folks at the "Hemisphere Regional Data Center" could theoretically match up the names to the phone numbers (not AT ALL trivial - I used to work with credit header data and telco record data - the data quality is an absolute shitshow), but that power certainly is not in the hands of any local law enforcement.