In response to a probe by the Federal Communications Commission, Google says its Google Voice service restricts calls to less than 100 U.S. telephone numbers, reports Reuters. And all those numbers Google believes are engaged in high-cost "traffic-pumping schemes."

PC Magazine notes that Richard Whitt, Washington telecom and media counsel for Google, admitted that those numbers:

generated more than 160 times the expected traffic volumes, and accounted for a whopping 26 percent of our monthly connection costs.

Whitt goes on to say:

We noticed an extremely high number of calls were being made to an extremely small number of destinations. To prevent these schemes from exploiting the free nature of Google Voice – making it harder for us to offer this new service to users – we began restricting calls to certain telephone number prefixes.