My RAZR V3xx has two screens, a small one on the "outside" and a larger one inside. During normal phone usage, the outside screen shows the Cingular logo. (Or the Motorola Logo if you have a non-branded phone.)
I decided to replace the Cingular logo with one of my own, so I used P2kCommander-v4.9.9 to replace the cl.gif file in a/mobile/ with my own. (I'm currently using the picture of electronics, which makes the outer screen look like a window into the phone, but I've included a few others you might want to use instead.) Remember to back up your original cl.gif if you ever want to go back!
A few images you might want to use on your phone:
Some originals in case you want to change back, or just change your provider: