<human>:  What have been some of the major milestones in the development of smartphones?
<bot>: Some of the major milestones in the development of smartphones include the introduction of the Apple iPhone in 2007, the release of the Android OS in 2008, the introduction of the Samsung Galaxy S series in 2010, the launch of the Apple App Store in 2008, the introduction of 4G LTE technology in 2010, and the emergence of 5G in 2019.