You can customize your Sidekick by downloading themes at the following sites:
Themes allow you to change the look and style of your sidekick 3 phone.
Normally a theme will allow you to change the background(s), the icons, the "bubbles" and hing sounds (sounds made when you open and close the phone).
There are a number of sites out there that allow you to upload themes you make or where you can download themes for free such as
skthemes.comskthemer.com or
sk3themes.com.
With the sk3 you can also change your keyguard (image displayed while locked) and your friend icons.
To learn how to create a hing sound, upload or create a theme, download and install a theme or anything else relating to themes you can
read this how to section.