Terranova has a great little piece up about what they say is "the inevitability of voice" in online gaming. Blizzard has talked (ha! I just made that up!) about implementing a voice chat system into the default client, but at this point, they don't really have to-- I don't think I can remember a higher level instance run that I've done in a long time that hasn't been accompanied by a Vent or Teamspeak server with my friends on it.
But the interesting thing about what Nate writes about online voice is that it's more than just being able to react quickly with strategy in a game-- with voice, we're moving ever closer to a deeper connection between our virtual and real identities. Part of the appeal of online gaming, way back in the beginning, was that players were able to keep their virtual identities separate from their real ones-- if you were an accountant during the day, you could hack and slash away at orcs all night, and no one from either world might ever know about the other.
But now, with voice chat, the people you play with get to know more than they ever have about the real you-- first and foremost, your gender, which is why some women still don't bother speaking on Teamspeak. But beyond that, I know much more about my guildies-- their age, their professions, their locations, their situation in life-- than I think I ever would have if I spoke to them only in text. More than ever, as voice chat is commonly and conveniently found in more and more games, it's not just how you play the game-- it's going to be how you sound as you do it.