Scaling Fonts

[Michael Doub]

I would like to create a mobile application where the user can increase and decrease the text in a field.  The field contains text on different font sizes for Title, Heading and basic text.

I am unsure how to work with fonts.   Do I need to find a font that has a wide range of sizes or are there scalable fonts?  How do fonts react on different screen resolutions?   This makes me wonder about how the text in buttons should be handled.  (So far I have only used icons)

I would appreciate if someone could point me in the right direction.

Thanks
   Mike