The ACLU just posted an article about a recent federal magistrate judge's ruling. It is a somewhat bizarre case. The DEA had an arrest warrant for a doctor suspected selling prescription pain killer drugs for cash. They then requested a court order to obtain his real time location information from his cell provider.
The judge went along, but then published a 30 page opinion stating that no order or warrant should have been required for the location information because the suspect had no expectation of location privacy. If he wanted privacy, all he had to have done is to turn off his phone (which would have prevented the collection of the information at all, not just established his expectation).
So, if this line of reasoning is picked up and becomes precedent, it is clear than anyone on the run needs to keep their phone off and / or use burner phones paid for with cash.
My concern is that, if there is no expectation of privacy, is there anything preventing government entities from requesting location information on whole populations without any probable cause or court order.
While I think that the use of location information in this case was completely appropriate, I would sleep better if there was the check and balance of the need for a court order before getting it.
This is another situation where technology has run ahead of the law. The Fourth Amendment was written in a time where information was in tangible form, and the only time it was generally in the hands of third parties, was when it was in the mail. Therefor search of mail in transit was specially protected.
Today, cloud and telecommunication providers serve much the same purpose as the US Postal Service, and are used in similar ways. It is high time that the same protection extended to snail mail be applied to the new high tech communications infrastructures we use today.