Simplify the following text for a Grade 11 native English-speaking person.
Original: The company initially made smartphones based mostly on Microsoft 's Windows Mobile operating system ( OS ) software , but in 2009 it began to shift its core focus away from Windows Mobile devices to devices based on Android OS .
Simplified: The company first made smartphones based on Microsoft 's Windows Mobile operating system , but in 2009 it started to make smartphones based on Android operating system .