I am not completely sure if the stock browsers on smart phones can it, but i assume firefox, opera, and now chrome (just realized to android recently) can handle css3 because css3 was built for smart phones and tablets in the first place. A browser that doesn't support it yet IMO isnt out of beta.
Media Queries deal directly with screen sizes, kinda like this...
if screen resolution = 320 width -> phone.css
if screen resolution = 640 width -> tablet.css
if screen resolution > 640 width -> main.css
so it is totally dependent on screen size, BUT with some new smartphones supporting big screen resolutions, im talking like 720p, I'm not sure how to fix it.