Is it possible to create a voice chat in ejabberd2?
May be, there are any features in this server, or there are any plug-ins to it for voice use.
Video and audio conferencing in XMPP only needs implementation in the clients. ejabberd doesn't need to implement anything for that.
Could you name the Jabber clients with audio conferencing implementation for whole chat room at once?
Well, I know you will soon develop a new client with support for audio conferencing in MUC rooms. And you will use that client with any MUC service. :)
This is being discussed in JDEV list today:
While developing XMPP Server and XMPP client for Video Conferencing, does XMPP Server need to support "jingle" ?
No, the server doesn't need to do anything for Jingle, just the clients.
You can join that list and make your questions.
Actually for conferencing server needs to support more than just STUN: RTP mixer/translator or something like that, there is the corresponding XEP for this.