You’ve read all of your free items this month. To register, get added benefits and unlimited access to articles, Become a Member. Already a Member? Sign in. Advertising Age Article Abstract Why U.S. Carriers Are Struggling In the Mobile Ads Business Telefónica's Launch of a Mobile Ad Exchange Could Prompt the U.S. Telecoms Further Along By Mark Bergen, Published on April 21, 2014 0 Want more Access, Content & Connections? Upgrade to Membership. We are glad you are enjoying Advertising Age. To get uninterrupted access and additional benefits, become a member today. Become a Member Already a member? Log in.