Google Voice has more than 1M customers. I read 1.2 and 1.4 - call it 1.3M.
BusinessWeek writes: "In its correspondence with the FCC, Google also reveals several companies that help it provide Google Voice. The list includes fiber-optic network operators Level 3 Communications (LVLT) and Global Crossing (GLBC). It also mentions Broadvox Communications, Bandwidth.com, and Pac-West Telecomm. IBasis (IBAS) is responsible for connecting outbound international calls on Google Voice and Neustar (NSR) provides "porting and carrier lookup services," Google says in the letter. Syniverse Technologies (SVR) provides the free text-messaging service."
By the way, GV is only blocking about 100 numbers to Independent exchanges that are traffic pumping.