Public interest in the means by which the government may collect telephone call records has been raised by revelations in recent years regarding alleged intelligence activity by the National Security Agency (NSA) and the Federal Bureau of Investigation (FBI). According to a USA Today article from May 11, 2006, the NSA allegedly sought and obtained records of telephone numbers called and received from millions of telephones within the United States from three telephone service providers; a fourth reportedly refused to provide such records. Additionally, a series of reports issued by the Department of Justice's Office of the Inspector General (DOJ OIG), most recently in January of 2010, indicate that, between 2002 and 2006, consumer records held by telephone companies had been provided to the FBI through the use of "exigent letters" and other informal methods that fell outside of the national security letter (NSL) process embodied in statute and internal FBI policies. These reports also indicate that records may have been sought without demonstrating a relationship to an active investigation. This report summarizes legal authorities regarding access by the government, for either foreign intelligence or law enforcement purposes, to information related to telephone calling patterns or practices. Where pertinent, it also discusses statutory prohibitions against accessing or disclosing such information, along with relevant exceptions to those prohibitions. The Supreme Court, in Smith v. Maryland , 442 U.S. 735 (1979), in a pen register case, has held that there is no Fourth Amendment protected reasonable expectation of privacy in records of telephone calls held in the hands of third party providers, where the content of any call is not intercepted. The Fourth Amendment to the United States Constitution guarantees: The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized. Whether the use of a pen register is a "search and seizure" within the meaning of the Fourth Amendment determines if the government, in compliance with the Constitution, must secure a warrant or court order prior to its installation. In 1979, the United States Supreme Court decided this question in Smith v. Maryland, holding that the Fourth Amendment does not prohibit the use of pen registers without a warrant. Writing the majority opinion joined by four other justices, Justice Harry Blackmun drew a distinction between the acquisition of contents of telephone communications using electronic listening devices, which the Court in Katz v. United States had deemed to be a "search" under the Fourth Amendment, and the capture of electronic impulses that identify the numbers dialed on a telephone using a pen register device. According to the majority in Smith , it is a constitutionally significant difference that pen registers do not record the contents of communications, in contrast to the listening devices employed in Katz . The Court explained that the Fourth Amendment does not apply to the use of pen registers because individuals do not have a legitimate expectation of privacy against invasion by government action, that protects the numbers dialed into a telephone system: All telephone users realize that they must "convey" phone numbers to the telephone company, since it is through telephone company switching equipment that their calls are completed. All subscribers realize, moreover, that the phone company has facilities for making permanent records of the numbers they dial, for they see a list of their long-distance (toll) calls on their monthly bills. In fact, pen registers and similar devices are routinely used by telephone companies "for the purposes of checking billing operations, detecting fraud, and preventing violations of law." The Court stated that telephone customers, by voluntarily conveying phone numbers to the telephone company and "expos[ing] that information to its equipment in the ordinary course of business," assume the risk that the company may disclose such information to law enforcement. Because there is no actual or legitimate expectation of privacy in the numbers dialed from a telephone, the installation and use of a pen register is not a "search" requiring a warrant under the Fourth Amendment, the Court ruled. In contrast, the dissenting opinions in Smith concluded that telephone numbers dialed from a phone are entitled to the same constitutional protection that telephone conversations receive under Katz because such numbers are not without "content" - they "reveal the identities of the persons and the places called, and thus reveal the most intimate details of a person's life." Furthermore, the dissenters objected to the majority's characterization that the use of a telephone involves an assumption of risk on the part of the customer that telephone dialing information might be disclosed to the government; assumption of risk generally requires there to have been a choice to engage in the activity, and "as a practical matter, individuals have no realistic alternative" to the use of a telephone. Although the protections of the Fourth Amendment may not reach records of telephone calls held by third parties, Congress has enacted a number of statutes since the Smith decision that both permit access by the government for foreign intelligence or law enforcement purposes to information relating to telephone numbers dialed from or received by a particular telephone number, as well as duration and usage, while simultaneously imposing limitations as to how such information may be accessed and under what circumstances it may be used. Information regarding telephone calling patterns, duration, usage, and length of service may be sought by the government directly through the use of pen registers or trap and trace devices. Statutory provisions authorizing, pursuant to court order, the use of pen registers and trap and trace devices exist in both the Foreign Intelligence Surveillance Act (FISA), 50 U.S.C. Section 1841 et seq ., and, for law enforcement purposes, in 18 U.S.C. Section 3121 et seq . Telephone calling activity may also be collected indirectly by seeking telephone toll or transactional records from third party providers. For example, FISA's "business records" provision, 50 U.S.C. Section 1861, authorizes court orders to compel the production of "any tangible thing" relevant to collection of foreign intelligence information not concerning a U.S. person, or relevant to an investigation into international terrorism or clandestine intelligence activities. Access to stored electronic communications is also addressed in 18 U.S.C. Section 2701 et seq. 18 U.S.C. Section 2702 prohibits voluntary disclosure of customer communications records by a service provider unless it falls within one of several exceptions. Required disclosure of customer records to the government under certain circumstances is addressed under 18 U.S.C. Section 2703, including, among others, disclosure pursuant to a warrant or grand jury or trial subpoena. 18 U.S.C. Section 2709 is a national security letter provision, under which a wire or electronic service provider may be compelled to provide subscriber information and toll billing records information, or electronic communication transactional records in its custody or possession in response to a request by the Director of the Federal Bureau of Investigation (FBI) if the Director of the FBI, or his designee in a position not lower than Deputy Assistant Director at Bureau headquarters or a Special Agent in Charge designated by the FBI Director in a field office, certifies that the records or information sought is relevant to an authorized investigation to protect against international terrorism or clandestine intelligence activities, provided that such an investigation of a U.S. person is not conducted solely on the basis of First Amendment protected activities. Finally, Section 222 of the Communications Act of 1934, as amended, 47 U.S.C. Section 222, restricts the voluntary disclosure of customer proprietary network information by telecommunications service providers. Violations of the pertinent provisions of law or regulation may expose service providers to criminal sanctions, civil penalties and forfeiture provisions, 47 U.S.C. Sections 501-503. Each of these statutory schemes is described in more detail below. Under 50 U.S.C. Section 1842, the Attorney General or a designated attorney for the government may apply for an ex parte court order authorizing the use of a pen register or trap and trace device to a Foreign Intelligence Surveillance Court (FISC) judge or to a U.S. magistrate judge designated by the Chief Justice of the United States to have the power to hear applications or grant orders approving installation and use of a pen register or trap and trace device on behalf of an FISC judge. The application must be approved by the Attorney General or a designated government attorney; must identify the federal officer seeking to use the pen register or trap and trace device; and must include a certification that the information likely to be obtained is foreign intelligence information not concerning a U.S. person or that the information is relevant to an ongoing investigation to protect against international terrorism or clandestine intelligence activities. An investigation of a U.S. person may not be conducted solely on the basis of First Amendment protected activities. The order must specify the identity of the person who is the subject of the investigation, if known. If known, the order must identify the person to whom the telephone line or other facility to which the pen register or trap and trace device is to be attached is leased or in whose name it is listed. In addition, the order must list the attributes of the communications to which it applies, such as the number or other identifier and, if known, the location of the telephone line or other facility involved. In the case of a trap and trace device, the order must also identify the geographic limits of the trap and trace order. Such an order, at the request of the applicant, also directs the provider of the wire or electronic service, landlord, custodian, or other person, to furnish any information, facilities, or technical assistance needed to accomplish the installation and operation of the pen register or trap and trace device in a manner that will protect its secrecy and minimize interference with the services provided. In addition, the order directs the provider, landlord, custodian, or other person not to disclose the existence of the investigation or the pen register or trap and trace device to anyone unless or until ordered to do so by the court.