According to internal estimates at Activision, Modern Warfare 2 made USD 310 million on its first day on sale - in the US and UK markets alone.
It's believed 4.7 million units were sold in the two countries that started midnight on November 10th 2009.

"The Call of Duty franchise has become a cultural phenomenon showing the power of video games as an entertainment medium."
"The shattering of these entertainment records is a testament to the compelling, cinematic and uniquely engaging experience that the Call of Duty brand delivers."

"Modern Warfare 2 has taken interactive experience to unprecedented heights setting a new standard for entertainment." --Mike Griffith, CEO of Activision Publishing.

Source: gamesindustry