This is the case that says so: http://en.wikipedia.org/wiki/Smith_v._Maryland
And these are the laws that allows it: http://en.wikipedia.org/wiki/ECPA http://en.wikipedia.org/wiki/Stored_Communications_Act
Somewhat unrelated, but under current law (the two above) they can read your emails without warrant too, but this was a big step: https://www.eff.org/deeplinks/2010/12/breaking-news-eff-vict...
"The spokesman also said that law enforcement agents have to obtain a court order for the data, except in special emergency circumstances."
But:
"The US Department of Justice has petitioned the 3rd District Court of Appeals for the right to request cellphone location data without a warrant."
http://thenextweb.com/us/2010/02/11/dept-justice-pushes-warr...
No, it doesn't.
If you're worried about NSA (llegal) spying in general, presumably the carriers retaining the data only makes it a bit easier for them. Since the info will need to be traveling around the network while you're active, they could easily just intercept that like they intercepted the voice calls.