sipXecs and in particular sipXconfig have been designed with skinning in mind. In many ways this goes along with localization where look & feel, logos, colors, and all the text are abstracted out of the application. 

The look & feel of the sipXconfig user interface can be customized as you would customize other Web pages.

The most basic skin consists of a new stylesheet, where sipXconfig abstracts all styles into stylesheets.

It is also possible to create a separately installabel component, such as an RPM or DEB, that includes a different skin. 

A good but more technical description of how this is done is on the Wiki .  More involved customization could aim at modifying the framework behind, which uses the Tapestry library. This allows changing the entire layout and move different elements around on the page.

Some examples on how this can be done are here. We are looking for help to create different skins.