A smartphone user shows the Facebook application on his phone in Zenica, in this photo illustration

A smartphone user shows the Facebook application on his phone in the central Bosnian town of Zenica, in this photo illustration, May 2, 2013. 
Facebook Inc's mobile advertising revenue growth gained momentum in the first three months of the year as the social network sold more ads to users on smartphones and tablets, partially offsetting higher spending which weighed on profits. REUTERS/Dado Ruvic (BOSNIA AND HERZEGOVINA - Tags: SOCIETY SCIENCE TECHNOLOGY BUSINESS)