In an interview with NBC News, Geoffrey Stone — who served on President Obama's five-person NSA review panel — made a surprising claim: the NSA doesn't collect metadata on every phone call. It doesn't even collect "anything close" to three-quarters of the calls made in the United States, despite what others have claimed.

NBC News' Michael Isikoff interviewed Stone, who is a law professor at the University of Chicago. Stone explained some new details of the development of the panel's reform proposals, including that the NSA was unable to demonstrate how the collection of metadata from phone calls helped prevent terror attacks. This was noted in the panel's report (released on Wednesday), but Stone went further with Isikoff, saying that the "results were very thin."

More remarkably, Stone apparently challenged the idea that the NSA sweeps up metadata about phone calls — for example, the numbers involved and duration — from every single call in the United States.

Although the NSA does collect metadata from major telecommunications carriers such as Verizon and AT&T, there are many smaller carriers from which it collects nothing. Asked if the NSA was collecting the records of 75 percent of phone calls, an estimate that has been used in briefings to Congress , Stone said the real number was classified but “not anything close to that” and far lower.

When the panel then asked the NSA why smaller carriers weren't included, Stone said that the agency responded by saying "they were setting financial priorities," which, Isikoff writes, was "'really revealing' about how useful the bulk collection of telephone calls really was." In other words: It wasn't cost effective for the NSA to set up programs with smaller carriers, in part because they didn't get good intelligence as a result.

It's a damning indictment of the metadata collection program, which already faces stiff opposition in Washington. And it's a bit of good news for Americans worried about the extent of NSA surveillance. Big Brother's watchful eye apparently has some blind spots.

Hat-tip: Justin Elliott.