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.
You may find this useful: