Shacknews confirmed the news with Microsoft which ultimately means that anyone who owns Universe at War, Shadowrun or Lost Planet: Colonies Edition on the Xbox 360 can play multiplayer online against 360 and PC Live members with a free Silver Xbox Live account. The catch being that this free Xbox 360 cross-platform gaming is more of a promotion and will only last until the rollout of the Fall update later this year. So, if you're part of the Silver crowd, own 360 versions of any of the games listed above and have the urge to play online, you better enjoy it while it lasts. Your freeloading time is limited.
[Thanks, to everyone who sent this in]