My development team is going to build a voice chat application.

Our plan is to use a pre-made library just for this purpose, but we haven't found any good one after days of searching the internet, so I thought I would consider a question here!

So the question is:
What library / project do you recommend? We are deadly serious with this, so it needs to be a good working one. Preferable an open-source one as well.

We have been looking at some XMPP libraries and projects, but none seems to be up-to-date, tested and well-documented.