http://news.cnet.com/8301-13578_3-10451518-38.html
"...the Obama administration has argued that warrantless tracking is permitted because
Americans enjoy no "reasonable expectation of privacy" in their--or at least their cell phones'--whereabouts. U.S. Department of Justice lawyers say that "a customer's Fourth Amendment rights are not violated when the phone company reveals to the government its own records" that show where a mobile device placed and received calls."