Is Smith v Maryland relevant to AP?
Here's a good response from the comments at Think Progress.
Matthew Rusk
The SCOTUS ruled in Smith v Maryland in1979 that who you call is not constitutionally protected because you have no expectation of privacy since you gave that number to the phone company. There is no constitutional need for a warrant, though Congress has the right to pass legislation requiring it (which I do not believe they have done). The AP is complaining that their First Amendment right as journalists are being threatened or interfered with, but they didn't seem to mind while private citizens have had their First Amendment rights to speech and free association threatened in the same way for almost 25 years.
http://thinkprogress.org/justice/2013/05/13/2005021/doj-yemen-aqap/
http://en.wikipedia.org/wiki/Smith_v._Maryland
Why The Department Of Justice Is Going After The Associated Press Records
http://www.democraticunderground.com/10022838537
Justice subpoenaed AP phone records, news service says
http://www.democraticunderground.com/10022838649
Leahy: I Want To Hear DOJs Explanation For Collecting AP Phone Records
http://www.democraticunderground.com/10022838804