Most of the time when I listen to a podcast, I look up the guest afterwards to see what they look like! Connecting a voice to a face makes me feel more connected to them and just gives you a better idea about who they are.
The inverse of this happens on Twitter where you see the faces and words of lots of people everyday, but you often don't know what their voice sounds like.
I think it would be cool to give Twitter users the option to add a short audio welcome note to their profiles. It could help make the whole place more human.
Twitter already have audio recoding built in, but only for tweets. I'm sure there are some ways that it could be misused, but I still like the idea!