Revelations about the practice triggered a national debate on privacy in this country.
The classified court order - first revealed in The Guardian newspaper - apparently allows the government to grab the phone data. The Republican chair of the House Intelligence Committee and a Democratic senator who was just briefed claim it has helped prevent a terrorist attack in America in the last few years.
They can't hear you, but they do know who you're calling -- when, where and for how long. A prominent senator confirmed a published report that the U.S. government requires Verizon Wireless - and likely other carriers - to turn over phone call data every day from every customer in the country.
"Who did you call and who did they call? And they have computer software that makes these little maps that show linkages," Richard Clarke, former White House counterterrorism advisor, said.
Clarke helped write the Patriot Act. He calls the cell phone data mining an extreme "overreach."
"Link analysis of phone calls always helps. It helps in drug cases and it helps in terrorism cases. But you don't need to have the whole country, all of our phone calls, in a database in order to do that. You could go to a court, the way the law was intended, and make your case and get a warrant," Clarke said.
Senator Dick Durbin - one of the president's biggest backers - calls the NSA program "disturbing" but "not surprising."
"We want to keep America safe but we don't want to compromise basic freedoms or privacy as individuals," Durbin said.
Senator Mark Kirk grilled U.S. Attorney General Eric Holder, asking how far the cell phone spying goes.
"Could you assure to us that no phones inside the Capitol were monitored of members of Congress?" Sen. Kirk said.
"With all due respect, Senator, I don't think this is an appropriate setting for me to discuss that issue," Horner said.
"I would interrupt you and say the correct answer is: 'No we stayed in our land and I can assure you we did not spy on members of Congress,'" Sen. Kirk said.
Just because the National Security Agency is collecting cell phone data that does not mean they are listening to calls. That would require a separate court order and likely be handled by the FBI.
As one analyst put it: What the NSA is doing is the equivalent of receiving boxes and boxes of records, storing them, but only opening the boxes and looking at the contents when suspicions are raised.