Jitsu is a multi-platform Free Software client with tight XMPP + Jingle support which, according to this article, works well as a secure Skype replacement. It also supports secure video calls, and SIP conference calling (see http://jitsi.org/index.php/GSOC2011/ConfCallChatting).
http://www.dominionpaper.ca/articles/4190
I'd like to try this out myself some time soon. Perhaps we could use the conf call aspect for larger scale participation in FSFE meetings etc.?
Sam.