Recently, I've been looking for a good way to talk between Linux and Windows with voice and possibly video.
Skype doesn't work well on Linux.
OpenWengo doesn't work well on Linux (yet).
Gizmo friggin owns -- it works identical to the Windows counterpart, as far as I know.
However, gizmo's icon is low quality. Here is a better one, in svg and png. E-mail me if you need help with using this icon.