The Unified Communications Interoperabilility Forum (UCIF) will be working on IPv6 testing of voice, video, instant messaging and other UC modes in the coming months. We've got an XMPP server (ejabberd 2.1.6) running on IPv6 now, and will be bringing up a SIP IP-PBX in the coming weeks. If you're interested in testing with these or other products over IPv6, let me know.