President Obama makes a distinction between the contents of phone calls and the information generated by the call (he calls it meta data, we used to call it transaction-generated data, and now it falls within the scope of big data), here is the analogy that is governing his thinking:
Mr. Pickering was targeted by a longtime surveillance system called mail covers, a forerunner of a vastly more expansive effort, the Mail Isolation Control and Tracking program, in which Postal Service computers photograph the exterior of every piece of paper mail that is processed in the United States — about 160 billion pieces last year. It is not known how long the government saves the images.
Together, the two programs show that postal mail is subject to the same kind of scrutiny that the National Security Agency has given to telephone calls and e-mail.
The mail covers program, used to monitor Mr. Pickering, is more than a century old but is still considered a powerful tool. At the request of law enforcement officials, postal workers record information from the outside of letters and parcels before they are delivered. (Opening the mail would require a warrant.) The information is sent to the law enforcement agency that asked for it. Tens of thousands of pieces of mail each year undergo this scrutiny.