- The phone companies know what number is dialed, and people know that because the phone company's equipment has to know where to route you.
- The phone companies keep a record of every call dialed, and people know that because they see it on their monthly phone bills.
People know that "pen registers" and similar devices exist, or at least the technology to trace a call exists, because the phone company can track down people who make harassing calls.
- Therefore, people shouldn't reasonably expect the numbers they dial to be private.
From the opinion:
Telephone users, in sum, typically know that they must convey numerical information to the phone company; that the phone company has facilities for recording this information; and that the phone company does in fact record this information for a variety of legitimate business purposes. Although subjective expectations cannot be scientifically gauged, it is too much to believe that telephone subscribers, under these circumstances, harbor any general expectation that the numbers they dial will remain secret.
What I'm wondering is whether there's any subsequent case law which questions whether the third-party doctrine holds when one of these tests is not true. I'm specifically interested in cases where #2 is violated, although I'd be interested in the others as well (e.g. a hypothetical secret machine that can read the contents of mail without opening the envelope).
My entirely untrained (and only moderately informed) opinion would be that because ISPs don't make it obvious in any way that they keep a record of what you do online (your monthly bill isn't broken down by website, for example), then the third-party doctrine shouldn't be applicable to them. Likewise, until Snowden brought attention to it, I would have expected most people to not know that their activity could be easily intercepted. Since there haven't been any cases making this point that I've heard of, I assume that either the cases have been quiet or there's a flaw in my logic and thus no one has tried.