The two major smartphone operating systems are Android and iOS (iPhone). Tablets are Android and iPadOS. See
iPhone vs. Android.
In the past, Nokia's Symbian OS was extremely popular, and more Symbian phones were sold around the globe than any other. However, in 2011, Nokia switched to Windows Phone, which Microsoft abandoned six years later (see
Windows Phone). See
iPhone,
Android,
BlackBerry,
Symbian and
how to select a mobile device.