Designing for mobile devices comes with its own set of hurdles and considerations, just like designing for the desktop screen.
All mobile browsers are not created equal, and you’ll need to be aware of their positive aspects and failures alike. Some mobile browsers allow you to zoom in and out of a page for easy access to links, some don’t. Some allow you to change the aspect ratio and some don’t. And of course mobile devices have varying screen resolutions, and are nowhere near the same as their desktop counterparts. If you thought designing for 800×600 years ago was painful, try 640 x 320 or lower.