The success of any mobile web application relies on design and performance. An entire book could be written about performance best practices especially when dealing with mobile web and native apps. However, there are some fundamentals that are important to review, because with PhoneGap you are actually working with a browser instance embedded in a native app.
When possible use small images to render the UI elements of your app. A very good approach is the one you can see in action when opening Gmail that uses small GIF files combined to render the user interface, ensuring a very short processing time. The images are not rendered directly in the UI; instead they are combined using different CSS rules. Furthermore, the images are usually grouped together and then rendered using a technique known as CSS Sprites.
Generally speaking, inline CSS and JavaScript are less expensive for the device, but they are not good practice at all. You can use the server to inject in...