I tried Gizmo a few nights ago and it works really well! The conference feature could be invaluable for global groups who need to keep in touch.
I’m probably one of the few people in the world who hasn’t used Skype so I can’t compare yet. Skype does offer almost-worldwide calls at 2c/minute I think but for calling the US, Gizmo is better at 1c/minute!
Even better, just like Skype, Gizmo also runs on Linux!
(Edit: the url for this entry has been updated because when I copy/pasted the title I brought over a strange “-” character that the post slug didn’t like! You should be able to click this entry now!)