Can the government track your cell phone's location without probable cause?

This is old news (September to December 2005), but seems pertinent today, as we learn more about the government's attempts to find and utilize new ways to learn about the activities of US citizens.  The EFF has been reporting on the government's efforts to track the location of cell phone users.  There have been cases in which the government has attempted to do exactly that, claiming they had no need to show that there was any reason to think that a crime had been committed.  

When is the government allowed to track your cell phone's location? What legal standards must the government meet before a judge can authorize such surveillance? That's the issue in two recent cases where two federal magistrate judges, in an unprecedented move, rejected Department of Justice requests to track cell phones without a search warrant. Setting aside the secrecy that shrouded these requests, the judges sharply rebuked the government. Both courts found the government's arguments completely unpersuasive, variously describing them as "contrived," "unsupported," "misleading," "perverse," and even a "Hail Mary" play. Yet, as the decisions further reveal, the Justice Department has routinely used its bogus legal theory to get secret authorizations for cell phone tracking from a number of courts, probably for many years.

Apparently, they do something similar with tracking credit card usage.  

Checking the links on the page linked above, we learn that -- interestingly -- the government has lost three out of the four cases that have been brought to court, and decided not to appeal the three that it lost.  They probably are waiting until the Supreme Court is effectively stacked with proponents of an imperial president.