First, third party doctrine is more limited than that, and in the event where a party is compelled to retain information and disclose it, third party doctrine b

First, third party doctrine is more limited than that, and in the event where a party is compelled to retain information and disclose it, third party doctrine becomes quite questionable (because they end up acting under the color of law). The thing is that usually CDR data doesn't require a warrant. The court ruled that since people are typically aware that the existance of CDR's and may rely on them for services from the telephone company, and because they are relatively non-revealing they do not constitute a search. The point is that the user of the telephone service discloses the calling information to the phone company and in such a way as to expect no privacy over the information. A similar case might be IP packet header information over routers, or photocopying address/return address/postmarks on the outside of envelopes passing through the USPS. None of these are considered to violate any reasonable expectation of privacy because, for example, we can expect that the address on the letter we drop of at the post office is publicly visible.