Voice is currently only available through an open webcam.
None of our sister sites offer voice only that im aware of so unlikely to see it here anytime soon as we slowly migrate to the much larger versions (check out our UK parent site if you want to see the direction that KS is heading).

Skype and programs like Ventrilo and Teamspeak are great things that can be utilized in conjunction with KS if you are keen to do that kind of communication only.
They offer free services with very good quality for the time being if voice is ya thing