The US government dipped into cellphone user accounts over 1.3 million times in 2011. Nine major US carriers (link) provided data released by US Rep.Edward J. Markey, co-chair of the Bipartisan Congressional Privacy Caucus.
"Information shared with law enforcement includes data such as
geolocation information, content of text messages, wiretaps, among
Carriers can be required to provide "cell tower dumps" of all calls & user data connected with an area tower in a given period; this includes location & data of many other people unrelated to law enforcement investigations.
There's very little judicial oversight of such activities. Rep. Merkey is reportedly concerned about what's done with the data collected.
The public also should be concerned: there's now no accountability as our private communications & on-line activities are monitored & exchanged among private sector technicians, the police, and ???.
The Electronic Frontier Foundation seeks to improve transparency and rule of law over such investigations. You can join or donate here (link). Don't wait and be too late...