Android combines the ubiquity of cell phones, the excitement of open source software, and the corporate backing of Google and other Open Handset Alliance members like Motorola, HTC, Verizon, and AT&T. The
result is a mobile platform you can’t afford not to learn.

Luckily, getting started developing with Android is easy. You don’t even need access to an Android phone—just a computer where you can install the Android SDK and phone emulator.
Hello Android 3rd Edition