Ventrilo is almost entirely based upon this need, and games have increasingly come to include built-in voice clients (including World of Warcraft, although its quality is rather widely debated).
Of course, hand-in-hand with the fact that we can talk faster than we can type, many of us have a clearer personality by voice than we do in text. We're more trained as human beings to react to audio cues anyway, as opposed to subtleties in sentence structure or the occasional "lol." So what do you act like when you get behind the microphone? Are you the one guy that won't stop making off-color jokes, or are you quiet and professional? Do you act the same way you usually do via text, or do you have a totally different side that only comes out over voice chat?