Facebook announced a new milestone yesterday for its spin-off messaging app Facebook Messenger: 500m monthly active users, which is up 150% on a year ago. Its growth isn’t a huge surprise, since the social network has been essentially forcing people to use Messenger by turning off the messaging feature within its main mobile app. But for some hints about how Facebook Messenger is going to develop, we recommend Wired’s interview with its boss David Marcus, the former CEO of PayPal. The future of Messenger takes in voice calls, payments and perhaps new forms of advertising: “Marcus wants to reinvent messaging between people and businesses, so that it’s useful to both parties,” claims Wired’s journalist. Something for music marketers thinking about the new wave of messaging apps and declining organic reach on Facebook to chew over, for sure.