Mobile css specific or device spefic

Hello - Just getting my teeth into mobile themes. We have a client who runs an eCommerce site and he wants a seperate theme for mobiles devices. The platform/operating systems we plan to build for are Apple iOS
, Google Android 1, 2 and 3
, Blackberry OS 4, 5 & 6, Windows Phone 7, Symbian OS 3 & 4.

My question is do we serve resolution-specific CSS files? I presume we would create a fluid design that scales horizontally to be able deploy a single design to many different mobile devices. Or do we serve device-specific CSS files? Where we have to check what device the visitor is using when they enter the site?

The other thing to consider is different mobile devices require different tools (Mice, joysticks, scroll-wheels, keypads, fingers.)

If anyone has done something similar and could provide some much needed advice that would be great :slight_smile:

Cheers