VX6100 and the Professionally Installed Car Kit
In other car kits I have had:
a) The phone attaches with a cable, you can "pick up" the phone while still charging and using the external antenna, and
b) Plugging in the standard headset overrides the speaker and just "works" as expected.
I realize that a) isn't possible due to the cradle design, but it seems like a software bug (I'm sure they will call it a feature) that the phone won't recognize the headset while plugged into the car kit.