In a survey conducted by the Interactive Advertising Bureau (IAB) and tech researcher Ovum, 19% of US mobile marketers said they planned to up their mobile ad budgets by 50% or more in the next two years. These respondents already market on mobile, and their responses suggest that they are seeing considerable return on investment (ROI) from the format. As advertisers plan their mobile strategy, they have choices as to what ad inventory to use. The study found that the greatest percentage of respondents - by a wide margin - employed mobile sites or landing pages, at 70%. The next most common type of mobile ad was a static mobile display or banner ad, used by 49% of respondents. Despite search’s ubiquity as a digital tactic - and its importance on mobile - a lesser 44% invested in mobile search ads. This may be in part because there is less real estate for such ads on mobile screens. Nearly three out of 10 marketers used branded mobile apps, and 19% used mobile video ads. There are still significant challenges mobile advertising must overcome, however. The greatest percentage of mobile marketers cited fragmented operating systems as their biggest challenge, followed closely by privacy concerns. Get the full story at eMarketer