Microsoft invented the MobileOptimized META tag to control the layout width for mobile markup rendered in Internet Explorer Mobile.
http://msdn.microsoft.com/en-us/library/bb159711.aspx
Mobile
Get access to data on 3,208,976 websites that are Mobile Optimized Customers. We know of 1,373,717 live websites using Mobile Optimized and an additional 1,835,259 sites that used Mobile Optimized historically and 762,453 websites in the United States.
Get a list of 3,208,976 websites using Mobile Optimized which includes location information, hosting data, contact details, 1,373,717 currently live websites and an additional 755,713 domains that redirect to sites in this list. 1,835,259 sites that used this technology previously and 762,453 websites in the United States currently using Mobile Optimized.