Themes designed for desktop PCs tend to look bad on smartphones. For one thing, the width of a smartphone screen is much less. Other issues include the need to avoid relying on mouseover actions (since there's no mouseover in touch) and the need for larger targets to be easier to tap (tapping a small link is much harder than clicking it). You may thus want your site to use a different theme for mobile users than for desktop/laptop users.

Go to Admin Panel -> Themes -> Add Themes and install the theme named 'Mobile', making sure you first de-check all the boxes next to it so that it's not as a default or exclusive theme. It's designed to wrap well at small widths, provide larger tap targets for the major elements (categories and listings can be tapped anywhere instead of having to hit a specific link) and underlines all hyperlinks for easy identification. You can customize it to your site as desired at Admin Panel -> Themes -> Manage Templates after installing.

Next you need to determine who sees the mobile theme. Relying on people selecting it themselves would be clunky, so WSN allows you to force all specified web browser user agents to use the mobile theme. Go to Admin Panel -> Themes -> Manage Templates -> "Mobile Version". Here's a suggested list of user agents:
Mobile
iPhone
iOS
Android
BlackBerry
HTC
Nexus