There are free facilities available for such services, the disadvantage is call quality or limitations on the number of participants allowed in the chat room. This isn't a suggestion to replace chat at all, quite the contrary. It merely serves as an option for people who want to talk and share their experiences in person should they wish. It's not always easy to put down in words one's experiences, especially if those thoughts are fleeting in nature.
As for privacy, the Nexus forum itself is catalogued by archive.org so even you delete an incriminating or sensitive post now, it may still be available via archive.org - don't believe me?
Why not take a look.
As for private voice related conversations, there's nothing stopping people eavesdropping on the text-chat page anyway. At least teamspeak allows password protected channels if one or more users that you know and trust wanted to talk about something personal (yes I know you can have private chats in nexus-chat too).
May I recommend that you
take a look first to learn a bit more about teamspeak as I have used this extensively in the past. Anyway, there's always the option of PM'ing someone in nexus-chat and having a Skype conversation with them, or any other preferred voip client related program, should you wish to utilise that option.
All I am saying is that it would be nice to have the option available if some of the people here, want to take advantage of it, and talk in person. Where else can one do this?