JetSetMe is a project that visually displays the roaming habits of mobile phones that operate on the O2 network. The company Provides the JetSetMe API that allows developers to create applications that make use of this data. In the United Kingdom O2, owned by Telefónica, is the second-largest telecommunications provider. JetSetMe taps into network resources to access the information necessary to understand how users move throughout Europe.
As a DC-area resident, I've been one of many local developers saying that the DC Metro needs some sort of API. If anything, just to be able to build or integrate transit routes into existing apps. The wait appears over and the Washington Metropolitan Area Transit Authority now has an API.