Here's one case where that didn't work out: http://jolt.law.harvard.edu/digest/telecommunications/united...

Using a phone without your name attached to it is not equal to anonymity: https://www.schneier.com/blog/archives/2009/05/on_the_anonym...

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.

http://www.nytimes.com/2013/09/02/us/drug-agents-use-vast-ph...