Barlow and I did an audio IChat AV session yesterday. Barlow has some interesting thoughts about this on his blog. When I was in Helsinki, Matt Jones also talked about how he kept Skype on all the time in the background with his partner who was in another country and felt her presence through the ambient sounds. Another person told me about how he listened to his daughter's piano practice on Skype.
My sister calls it "ambient virtual co-presence" in her paper (pdf) about Japanese mobile culture. She talks about this in the context of texting and talking on the mobile phone. She discusses how the value was not always in the content being exchanged, but in the fact that people felt connected when they were constantly exchanging traffic. The "connection" can be IM, voice, text messages or just about anything that allows you to feel someone's presence.
Over a decade ago, Barlow blew my mind with his essay, "Selling Wine Without Bottles: The Economy of Mind on the Global Net" I think the next one is, "It's not the wine, it's the company" or something.
As Barlow points out, when all this stuff becomes literally free, we can do it "always on" instead of being so m-time "hello/goodbye" about phone calls. I do think audio will become a part of presence. My sister focuses on how mobile computing is a seamless part of our real world instead of the traditional "real life/cyberspace" notion of something we are either in our not. I think combining these two things is an area that will really change the way we live our lives for better or for worse.