It was a long time coming, but back in February Skype made it onto Windows Phone in beta. Now, testing is over, and you can get your hands on the full, official version from the WinPho Marketplace.
Unlike the beta, the app would work best with particular phones, no such caveats seem to have been put forward for this official release. As ever, the charms of video and voice calls over WiFi or 3G are hard to turn down—so cheap!—and it looks slick enough on WinPho, too. You can download the app here.