I have three different versions of a mobilized website, and as the market is flooded with more and more phones, I\'m struggling to keep up with knowing where to push them. I\'m
I'd use http://www.modernizr.com/ Modernizr to detect the capabilities in the client, and then redirect to a different location in case support is insufficient for the current fidelity-level.
If there is no CSS/JS support at all, you're pretty much screwed when it comes the client-side part. You'll have to resort to things like useragent sniffing... but then, nearly all phones have at least rudimentary CSS support, even the fairly old models.