For plone 4.2.5 is there a non-complicated way to set up theme switching between desktop/mobile versions based on visitors screen size? 
Something like "if less than 640x480 then" serve the mobile version ? 
Talking about 2 non-Diazo themes for instance?

What is ++skin++ for skin switching, may it work?

I am quite new to plone and not really a programmer so a "sane" solution would be really appreciated !