A new report projects that mobile ad spending in the US will total $14.9 billion in 2014 and surpass desktop ad spending by 2016, reaching $28 billion. Mobile search currently generates the most revenue, with Google the top player and Facebook second. A study found that mobile shoppers visit more shopping sites than desktop users, particularly on weekends and nights, and prefer brand and coupon sites over reviews. Spotify will launch free music streaming on mobile devices, using an ad-supported model similar to Pandora.