Today is D-Day for Microsoft’s Windows Phone 7 mobile operating system. The desktop software giants [A1] are launching their highly-anticipated and revamped mobile OS through various carriers across most of Europe, and boy do they mean business. Remember that $1 billion WP7 and Kinect marketing blitz we told you about? Well, Microsoft is giving away all sorts of freebies, in an effort to drum up sales. Earlier today, the Redmond outfit was spotted giving away Microsoft-branded Skull Candy headphones to customers at the Orange outlet on Oxford Street in London. Spain’s Movistar and Austria’s A1 carriers are reportedly giving away free XBox 360s to early adopters of WP7 (subject to signing a 2-year mobile contract). Windows Phone 7 launches in the U.S. on November 8, will all the marketing hype pay-off?