Tweeted by French site
Gameinmotion, are supporting pictures of what
may exist in the near future as a compilation for the Call of Duty: Modern Warfare trilogy.
Based on the title of the package and interior of the steelbook case, it will most likely be packaged with the 3 Modern Warfare games in the series. As this is not (yet) announced officially by Activision, it can be treated as a rumor with a good possibility of coming true.
Obviously there are no official details released for this and it can only be assumed that these will be released for the console (Xbox360 & PS3) and PC platforms. And there's a good chance this will be a worldwide release also.
But for now, just drool all over these glorious pictures:
Shiny Steelbook with embossed 'Call of Duty' title

Pictures indicate this will house Call of Duty: Modern Warfare, Modern Warfare 2 & Modern Warfare 3 games

2011 prints can be found inside the cover*
*[Note: Although a Call of Duty: Modern Warfare Collection is already in existence, that particular package contains two CoD: MW games in two separate standard game cases released in 2010. This '2011' edition will be packaged in one steelbook case instead.]
All credits go to Matrix6 for writing and pointing out!
Source
*UPDATE* 8/20/2011
mackalaway, who works for Micromania in France, provided some additional deatils. This is an official SteelBook case and it will be sold as just a stand-alone case by Micromania at a price of 9.99 ?.

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