Security → Phone Meta Data can reveal sensitive information

NSA collects meta data for all phone calls but not content. Meta data can reveal very sensitive personal information depending on the phone numbers called and patterns to calls. Content is not needed to reveal sensitive information if a woman calls a rape hotline or someone calls a suicide prevention hotline or a government employee suddenly begins calling an investigative reporter or someone calls a hotline to "anonymously" report child abuse. It becomes even more revealing in bulk.

»www.washingtonpost.com/b ··· secrets/
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When governments fear people, there is liberty. When the people fear the government, there is tyranny. Thomas Jefferson

Which is precisely why NSA harvests the metadata. Skilled analysis of a user's comm traffic patterns will quite often tell the analyst much more than the actual transcript of a given conversation. Such exploitation of 'metadata' goes back to primitive times and the observation of who or what comes in and out of a walled city in order to assess its strength and the possible intentions of its inhabitants. Electrical/electronic communications merely facilitate the process for security and military agencies.
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The American Republic will endure until the day Congress discovers that it can bribe the public with the public's money. -- A. de Tocqueville