Facebook has managed to gather 1 in 5 of its global ad dollars through its mobile platform, according to Kenshoo Social. Android smartphone devices dominated Apple's iOS by bringing in 71% of the spend, with iOS crushing Android on the tablet side at 97%. Cost-per-click for mobile devices ended December at $1.38, compared with desktop's 81 cents. Cowen and Co. predicts that Facebook's mobile-ad revenue will hit $1.7 billion this year, compared with $4 billion on the desktop.