Imagine if you had data on all cell phones, including location at time of call - wouldn't it be remarkably easy to match a disposable phone with it's predecessors based on when and where it was used, and who it was used to contact? For how, see this article: http://justsecurity.org/2013/10/11/nsa-call-records-database...
> The [Hemisphere project] slides emphasize the program’s value in tracing suspects who use replacement phones, sometimes called “burner” phones, who switch phone numbers or who are otherwise difficult to locate or identify.
