The document discusses several major mobile operating systems:
1) iOS powers the iPhone and has an app store with over 185,000 apps downloaded over 4 billion times. It uses a layered architecture and about 500MB of storage.
2) Android is an open source software stack owned by Google and the Open Handset Alliance, based on the Linux kernel. It has a large SDK and apps developed by Google.
3) Symbian is an open source OS contributed to by Nokia and others. It uses a microkernel architecture with drivers and services in separate layers.