The New York Times and Pro Publica have each published detailed reports describing massive, voluntary cooperation between the NSA and AT&T.
New York Times
Excerpt from the New York Times reporting:
The National Security Agency’s ability to spy on vast quantities of Internet traffic passing through the United States has relied on its extraordinary, decades-long partnership with a single company: the telecom giant AT&T.
While it has been long known that American telecommunications companies worked closely with the spy agency, newly disclosed N.S.A. documents show that the relationship with AT&T has been considered unique and especially productive. One document described it as “highly collaborative,” while another lauded the company’s “extreme willingness to help.”
AT&T’s cooperation has involved a broad range of classified activities, according to the documents, which date from 2003 to 2013. AT&T has given the N.S.A. access, through several methods covered under different legal rules, to billions of emails as they have flowed across its domestic networks. It provided technical assistance in carrying out a secret court order permitting the wiretapping of all Internet communications at the United Nations headquarters, a customer of AT&T.
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After the terrorist attacks of Sept. 11, 2001, AT&T and MCI were instrumental in the Bush administration’s warrantless wiretapping programs, according to a draft report by the N.S.A.’s inspector general. The report, disclosed by Mr. Snowden and previously published by The Guardian, does not identify the companies by name but describes their market share in numbers that correspond to those two businesses, according to Federal Communications Commission reports.
AT&T began turning over emails and phone calls “within days” after the warrantless surveillance began in October 2001, the report indicated. By contrast, the other company did not start until February 2002, the draft report said.
In September 2003, according to the previously undisclosed N.S.A. documents, AT&T was the first partner to turn on a new collection capability that the N.S.A. said amounted to a “ ‘live’ presence on the global net.” In one of its first months of operation, the Fairview program forwarded to the agency 400 billion Internet metadata records — which include who contacted whom and other details, but not what they said — and was “forwarding more than one million emails a day to the keyword selection system” at the agency’s headquarters in Fort Meade, Md. Stormbrew was still gearing up to use the new technology, which appeared to process foreign-to-foreign traffic separate from the post-9/11 program.
I think this tweet summarizes the relationship rather well:
The arrangement between the two entities should be carefully examined for constitutional violations. The report was based in part on files provided by whistleblower Edward Snowden.