If you search the layout files, you should find that image is located in the following file:
You then need to find this code:
<block type="core/template" name="left.permanent.callout" template="callouts/left_col.phtml">
<action method="setImgAlt" translate="alt" module="catalog"><alt>Our customer service is available 24/7. Call us at (800) DEMO-NUMBER.</alt></action>
All you need to do is change the path between the <url> tags from checkout/cart to wherever you want it to go.
Hope this helps.