In June 2009, Google Voice began noticing extremely high cost calls to a concentrated number of destinations. Our internal investigation revealed that the top 10 prefixes to U.S. destinations (NPA-NXX) accounted for l.l percent of our monthly U.S. traffic by volume – an unusually large number, and some 161 times the expected amount by prefix. In tum, this traffic accounted for 26.2 percent of our monthly U.S. cost – again, an unexpectedly large number. In addition to these grossly anomalous call patterns (which include the frequency and duration of calls to rural areas), we also were aware through various industry sources of certain in-bound traffic stimulation practices, and the identities and locations of some of the carriers in question. Many of these businesses are located in rural areas with local carriers that charge unusually high rates for terminating traffic. Our own underlying carriers would assess Google Voice up to 39 cents per minute for some of this interstate traffic. As a result, based on an application of these data filters to the total universe of our outbound traffic, in August 2009 Google Voice began the practice of restricting calls to certain high-cost destinations. Currently, fewer than 100 U.S. telephone numbers are restricted based on an application of these filters.