I am assuming it is OK to post cell info. from a MSM article as long as you don't give as long as I don't give my personal opinion as I am not considered an expert in the field? If not Mods, please delete.
http://www.propublica.org/article/thats-no-phone.-thats-my-tracker
"Cellular systems constantly check and record the location of all phones on their networks and this data is particularly treasured by police departments and online advertisers.
Cell companies typically retain your geographic information for a year or longer, according to data gathered by the Justice Department.
Turning it off when youre not using it will also help, because it will cease pinging your location to the cell company, but are you really going to do that?
Shutting it down does not even guarantee its off malware can keep it on without your realizing it.
The only way to be sure is to take out the battery."