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 3,564,387 websites that are Mobile Optimized Customers. We know of 1,588,772 live websites using Mobile Optimized and an additional 1,975,615 sites that used Mobile Optimized historically and 911,952 websites in the United States.
Get a list of 3,564,387 websites using Mobile Optimized which includes location information, hosting data, contact details, 1,588,772 currently live websites and an additional 913,255 domains that redirect to sites in this list. 1,975,615 sites that used this technology previously and 911,952 websites in the United States currently using Mobile Optimized.