A lot has been written about whether the NSA monitoring of the phone numbers Americans call is unconstitutional or otherwise illegal.
As I have explained elsewhere, monitoring of the numbers we call (and the addresses to which we send emails) is not unconstitutional but should be unconstitutional.
I analyze this issue in The Fourth Amendment in an Era of Ubiquitous Technology, an article I presented at a Fourth Amendment symposium last year. The bottom line is that the Supreme Court inexplicably got all this wrong almost 30 years ago, when it held that the Fourth Amendment does not apply to the use of a pen register to track the numbers dialed from a telephone, even a telephone in someone's home. The Court held, basically, that because we know the phone company gathers this information, we have no right to expect that it will not be given to police.
As many recognized at the time, the decision was wrong when it was issued. The Justices who signed on to the decision concluded that we know we are exposing "private" information to the phone company and, in so doing, assume the risk that it will voluntarily share this information with law enforcement. The Justices who dissented, notably Justice Marshall, pointed out the fallacy in this conclusion: The notion that we assume a risk is based on the premise that we have a choice -- here, to share or not to share this information with the phone company.
As Justice Marshall pointed out, we really have no choice. Our only options are (i) to use technology and run the risk that information about our use will be shared with the government or (ii) to become a Unibomber-style Luddite who does not use telephones . . . or email and other technologies, because the decision applies to any information we share with third-parties.
History is vindicating Justice Marshall and the other dissenters. Unfortunately, I fear it will be a very long time before the Supreme Court re-considers this issue (and, one hopes, gets it right this time).