I just tried the combination of web-based Gmail <-> iChat and the web client can see that the iChat client has a camera and I can initiate a call but iChat never shows an incoming one.
If I go iChat<->iChat over Google's XMPP server I can make a call. Does iChat speak yet another incompatible video call extension if it used with an XMPP network?
Adium can't do AV either.... Can anyone recommend a OS X client? Video chat is currently the last thing that stops me from uninstalling Flash.
iChat in Lion will features service plugins.