Changing the voice used for navigation on an Android phone from robotic to something more natural is easy, but buried in the menus.
View this video how-to.
First hit the menu or options key on your phone and select settings.
Scroll down to accessibility.
Then scroll down to text to speech options.
Depending on what is installed on the phone, there may be a few options listed. The phone will typically default to the manufacturer's voice option.
By tapping on the gear, users can change language settings for the default voice, but for the more natural text to speech synthesis, choose Google text to speech engine.
There are also applications in Google Play that will allow for more voices and languages.