In November 2007, Google announced the first open platform for mobile devices: Android. Around a year later, in September 2008, T-Mobile announced the G1, the first smartphone on the Android system. It was later expanded in 2011 with the release of Android 4.0 Ice Cream Sandwich to also work on tablets. In September 2013, the Android system hit 1 billion device activations.
For a little bit of perspective of the program's growth: Apple, in comparison, announced 500 million devices this past January, five months after Google hit the same mark.