That's like saying that just because the government is allowed to walk by your house and see if anyone is home without a warrant, then a webcam pointed at your front door should be broadcasting on the Internet. The fact we don't do the latter isn't a valid argument to justify requiring a warrant for the former.

Since there are degrees of privacy, "not private" for the purposes of the 4th amendment doesn't necessarily mean "totally public." The line that has been drawn is that if information is "not private" enough to share with your thousand closest friends at AT&T, it's "not private" enough for the government to see it without a warrant.

With regards to meta-data, you don't even have to get into the whole expectation of privacy inquiry. It's not even your data, it's AT&T's data. The 4th amendment explicitly states that people will be secure in their houses, persons, papers, and effects. That implies ownership or at least control. But call metadata is AT&T's property; the digital records are their papers, generated by their computers, for their internal purposes. If it were up to you, you probably wouldn't even want those records to exist, but they do, because they're not yours.

Regardless of where you draw the line on public versus private, it's clear you cannot have a reasonable expectation of privacy in someone else's property.

Don't get me wrong: I wish Congress would pass a law requiring telecoms to erase such data immediately, keeping only aggregate data for billing purposes. But the Constitution says what it says, not what you want it to say.