These networks are already "laced with VoIP," as Matt puts it.
Matt's Playing Games with VoIP article, out this week, quotes Jupiter Research analyst Joe Laszlo as saying that "all the video game system manufacturers are looking at ways to expand their communications capabilities,so there's reason to believe that a console or gaming network could become a central hub for other forms of communications technologies," including VoIP."
Matt also quotes Yahoo! vice-president of communications products Brad Garlinghouse as saying essentially the same thing.
"It's not the same thing as being a Skype or Vonage, but these people (the gaming platform builders) are using VoIP technology to communicate, so you have to consider how they might try to take advantage of that."