For what it's worth, you should be able do this with almost any phone that has a stereo headset jack, though you may need a (fairly inexpensive) adapter cord. The adapter cord may or may not have a microphone and answer/hang-up button.
I've done this with a Nokia E71*. The only really awkward part is that you need to hold the phone near your face to talk -- or, you could shout if that's easier.
It does allow me to listen to streaming audio (Nokia has a good Shoutcast client available for their phones), voice navigation instructions (I have my quibbles with Nokia Maps, but it's ok for what it is), and still take phone calls.
*unlocked, on AT&T Wireless. The E71x (AT&T branded and carrier-locked version) should function similarly.
-Rusty