The number of Android devices that have been activated around the world since the launch of the OS in 2008 has surpassed 500 million. Google’s director of product management for Android, Hugo Barra, posted the news on the Google+ social network and added that 1.3 million new devices are being activated every day.

Research firm IHS iSuppli meanwhile has forecast that cumulative shipments of Android smartphones will break the 1 billion barrier in 2013, just five years after the OS was first launched.

Annual shipments are forecast to reach 451 million by 2013, up from 357 million this year, meaning the total number of Android devices shipped since 2008 will hit 1.1 billion by the end of that year. If the current rate of growth in Android shipments continues, total shipments will approach 3 billion by 2016.

IHS mobile analyst Daniel Gleeson said the success of Android is largely down to Google’s growth strategy based on providing the OS as an open-source platform for third-party smartphone makers for free.

“Such an open-source model means that Google offers handset makers the ability to customise Android easily, and by also eliminating licensing fees, is greatly encouraging adoption among smartphone handset manufacturers,” he added.

In contrast, devices running Apple’s iOS are forecast to reach 527 million cumulative shipments in 2013, not hitting a billion until 2015.