Voice action is one of the most unused built-in features of the Android, probably because of its weak advertising and unawareness. Available in Android 2.2 and higher, Voice action allows you to control your Android phone or tablet with your voice; letting you do common tasks such as calling a contact, browse the web, send sms, view maps, and listen to music.
To do a Voice Action open the Google Voice Search application. This is not a traditional app and is hidden in most of the standard application menus. You can open the Voice Action app by adding Google Search widget on the home screen and clicking the microphone icon(shown to the left) or by clicking this link on your Android device.
Here are all the actions that are currently available: