Ok, as I promised...
Now I have to say a few things. First off, I've never really done any sort of interface like this, so go easy on me. Secondly, there is some possible explanation needed for what is going on?
The first phone is showing the normal interface you'd see while listening to a song.
The second phone is showing what happens when you're listening to music and you get a call. The icons and text on the screen dim, except for the date/time and menu bar, and the person calling (or number if it's not in your address book) appears and below is a picture (again, if available) The iTunes play symbol has also changed to a paused symbol, to indicate that you're not listening to music because there's a call. I'm guess you'd either open the phone, or simply press the center click wheel button to answer the call. Those things would obviously be worked out.
Lastly, the phone on the right is just a display of how entering numbers would look. Again, things like address book entries would all be accessed through pressing menu, where an almost identical iPod layout would appear, but instead of only having Music, Settings, etc., it would also have things related to the Phone like Address Book, Camera, you get the idea.
Feedback is welcome, as always. I also have more ideas that I hope to work on in the next few days. Thanks!