Searching around for headphone adapters, I came across the following site:
http://www.pocketpctechs.com/ppcthsa.asp
Looks like you can have your nice 3.5mm phones plugged in to listen to mp3's etc, then answer the phone using the button - no need to unplug!
Anyone tried one of the adapters with a built-in mike on the 600? I called the company and they didn't know if the units they currently have (for other devices) would work. Anyone know the compatability issues?