The user interface on that example is based on the jQTouch Javascript library. It executes functions on the lwIP web server via DHTML. This book is a good overview on how to use jQTouch to develop iPhone front ends.
http://www.amazon.com/gp/product/0596805780Building iPhone Apps with HTML, CSS, and JavaScript
There is an online version of the book on O'Reilly's web site.
http://ofps.oreilly.com/titles/9780596805784/You can also look at jQTouch docs and examples at
jqtouch.com. If you are comfortable with Javascript, modifying the iPhone interface on the enet_io example should be fairly simple and will allow you to implement a nice mobile interface to your embedded application.