The good news is that if you support 4.1, it is simple. Check out this link and scroll down to the fonts for full details, but basically you will have three font families (Roboto, Roboto Light, RobotoCondensed) to choose from and four styles for each (normal, bold, italics, bold italics).
In XML, you can simply use standard text attributes:
android:fontFamily="sans-serif" android:fontFamily="sans-serif-light" android:fontFamily="sans-serif-condensed" android:textStyle="bold" android:textStyle="italic" android:textStyle="bold|italic"
Or programmatically, you can purchase them like this:
Typeface robotoLightItalic = Typeface.create("sans-serif-light", Typeface.ITALIC);
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