I installed Skype Mobile on my Droid last night which allows me to make Skype-to-Skype calls for free. Thought at first it might be billed to my phone minutes, but nope, confirmed it this morning, Skype-to-Skype is free and unlimited.
fosteronfilm and I play in a cross-country D&D 4E game on Fridays run by dude_the with teflaime and dean13. We use Skype to conference call all of us together and MapTool as the tabletop emulator. I usually run two machines for it, my VAIO laptop for Skype and our old, clunky HP laptop, with its much larger screen, for MapTool. (The HP is somewhat ancient and has a tendency of throwing a hissy fit if I try to run both Skype and MapTool on it.)
Thinking about trying Skype for our gaming tonight on my phone so I don't have to have quite so many machines going. Although, admittedly, there is a certain geek-joy in being surrounded by all that glowy tech.