I have a Zune and haven't used it since I got the EVO. It's pretty much equal in quality. The battery on the Zune lasted longer than the phone though, that's the only down side.
If you get a call it just silences the music and plays the ringtone. Then when you hang up the music resumes.
If you get a text the music will stop for a second while the text notification plays then right back to normal.
[><] Deo Vindice [><]