I created this because I really needed something interactive to debug my PhoneGap iOS project. There is a similar project out there called ibug but it is no longer working.
You can get the code here, and below is a quick screencast.
Edit: Turns out it was unnecessary. I kept searching for Mobile Firebug before I came to the conclusion that I need to write one myself. But someone from the PhoneGap user group told me there's actually a Mobile Web Inspector out there. It's good enough for me for now, although I have to say I don't really like the Java server code in there... looks overly complicated to me.