Mobile phones are too short in terms of vertical width to show grid-based category pages or "product walls" - even at only two columns wide, you will only see a slice of the product image, let alone the title, price and five-star reviews. If you go to three columns the images become too small to be appealing and persuasive.
I can't advocate a separate media query for every device from table on down, so I'd shoot for the best size that displays at all levels
My Android G2 has 3.7 inch, WVGA 800x480 display which is a .60 aspect ratio. That's fine, although not as great as a .667 or .75 ratio found elsewhere - like the iPad 2. The problem, though, is that when I'm in portrait mode I only get a miniscule except that it is only
iPhone 4S 960x640 3.5" .667
Blackberry Curve something like a 2.4" and that might have navigation controls showing too, 320x240 = .75 aspect ratio