Illustrator :: Create Designs On Artboard That Matches Screen Size

I create the designs on an art board that matches the screen size of whatever device I'm designing for, for instance 320x480px. The problem comes when I want to read the font sizes used in the design in order to apply them in the actual mobile app. Illustrator seems to use a strict 1px = 1pt rule. That means a 12pt font in Illustrator is always 12 pixels. This is however not true on the mobile device, which uses some other ratio. This means I have to "guess" the font sizes, trial-and-error style, which is ridiculous.
 
I've tried downsizing the art board, to something like 240x360 px, and then the font sizes do better represent those on the mobile device, but then all the graphics does not. So that's a no go.
 
Is there any way I can define in Illustrator the ratio between pixels and points? It seems Illustrator only supports a default 1 pixel = 1 point setting? (In Photoshop, for instance, this is not a problem as you can set the intended physical size of the document independently from the pixel grid. Any way to do this in Illustrator? Does Illustrator simply assume pixels is a physical unit, like inches and points?