Although Microsoft has acquired Skype, this popular voip application is not the first to be ported over to it’s own Windows Phone 7 platform. Instead, Tango, a new kid on the block is now available on WP7.
You can now make free video calls to your friends on WP7, iPhone, iPad, Android. You can download it at the link below or at the marketplace on your mobile handset.
http://www.tango.me/get-tango/