I have voices inside my head, too. It never occurred to me to talk to them on purpose or really try to pay attention to them until recently, because I've always been like that and I thought it was normal. I brought them up to my new T just before we ended on my first visit, so I have no idea what she's going to say about it -- she just said it wasn't normal.
Mostly they just do their own thing, talk to eachother, comment on things I'm thinking or doing, etc. Sometimes it gets pretty loud in my head!