How to Put an SMS wallpaper on the iPhone
Most people find the default SMS background for the iPhone fairly dull, so why not spice things up? Thanks to Cydia and some clever hackers, there is now a way to modify the background of your text messages!
Here is the source that needs to be added to Cydia: http://iphonesch.iespana.es/repo/
From there, just follow the rest of the information provided in the video. Good luck!