If you had a location that was a known drug hot spot, you could use this data to see who frequented that location. Using that info, you could use "good old fashioned police work" to contact each person and get them to roll on someone else. That's much easier than sitting in a stakeout trying to ID those that come and go.
Or you watch them, find out where the stash house is, and call in an "anonymous tip" to another agency. They get a warrant, raid the stash, and it's all above board (or near enough).
Parallel construction makes the mere existence of these data sets extremely dangerous.
Better hope the defense attorney doesn't ask who the caller was. Parallel construction is actually not legal and can result in evidence being inadmissible.
If the answer is "we don't know, they didn't leave their name" then it's deniable if not actually legal. That's a pretty low bar to jump. This anonymous tip --> raid scenario happens all the time, it's called "swatting".
What "anonymous" tip line run by law enforcement is not capturing caller ID and any other location that can be garnered during the call? If there are any, I'd say that is a total failure on the agency in question.
And if you call such a line from an identifiable device, such as your home or work land line or your cell phone, then you should absolutely expect to be identified! I assume someone who is motivated to remain anonymous would take the necessary precautions to do so. I don't think that's unreasonable?
