One of the little known secrets for years was that Microsoft was one of Level3’s VoIP customers. I remember talking back in 2005 to Level3 execs (many now departed) about MSFT being a VoIP customer. They were amazed as all MSFT did was run voice over their data network for XBOX Live, without telling Level3.
This is much like having Skype on the Sony Mylo, but with a slightly different twist.