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 Foursquare May Actually Be Worth $600 Million But Only If It Starts Charging Brands for Access -- and Soon By Kunur Patel, Published on June 24, 2011 2 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. Register Now Already a member? Log in.