From Dark Reading online magazine...

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JUNE 5, 2006 | Upset about the National Security Agency's call record

If you're a mobile phone user, you may have more cause for concern than
the average landline user. Turns out, mobile phone records can reveal
not only who you called, but location technology onboard the mobile
phone and at the carrier network can reveal where you made the call and
everywhere else you went too.

....if the carriers are already passing on confidential details without a
warrant, then they could just as easily be handing over subscriber
location information.

"The fact of the matter is, if they're handing over call records,
there's nothing to stop the hand over of that material as well," says
Winkler. "It would be okay if they were to get warrants for it. There's
nothing to stop people if they're not going to put limits on it."

[more in article]

See More: NSA call records redux