Gear Live found a roundabout, but clever, way of streaming Zune tracks onto your iPhone. Why would you do that? Because Zune Pass gets you a basically unlimited amount of songs, and they don't play natively on the iPhone.
What you do is set up Orb on a Windows machine to transcode, on the fly, your already downloaded Zune songs. This way you can listen to your music (your entire music library, not just 16GB or 32GB worth) wherever you have an internet connection. It works over 3G as well as Wi-Fi, but EDGE is a little too slow for full-quality music.
Head over to Gear Live for a walkthrough. [Gear Live]