The themes of the SonyEricsson phones e.g. T68 and T610 can be modified. A theme file (.thm) is a tarred xml file with images. There is a nice solution for Windows [1] and one for Linux [2]. There is also an editor for Mac OS X [3].
[1] http://members.lycos.co.uk/themecreator/
[2] http://www.thai.net/gnulinuxt68i/default.htm
[3] http://homepage.mac.com/tobiaslidskog/T68ThemeEdit/
