Given the aggressive push by Google, Android mobile phones became the most fierce and perhaps the only worthy competitor to Apple's iPhone. Android has seen several iterations and given its open source nature, manufacturers have been able to customize the OS as per their needs. Today, every major phone manufacturer has their own UI pasted over Android.
With the smartphone revolution coinciding with the mobile boom in India, it is a valid question to ask which smartphone platform(s) sells the most. Symbian did well for several years in India, however, with the touchscreen boom, Android is the platform of choice in India. With increasing number of tablets and smartphones in the low / mid range, Android's growth is getting faster by the day.