Microphone quits working randomly

I'm trying to use a bluetooth headset with my PC for VOIP.
I've got a desktop and two laptops that do the same thing.
All are windows 2K SP4.
Cardio headset
C-Tech BT101 headset both do the same thing.
CQPhone and picophone do the same thing.
Bluetooth software is by Windigo and came with the
Cyber-blue usb dongle, claims to be Bluetooth 2.0.

The connection works initially, but after a random
interval ranging from a few seconds to a few minutes,
the microphone quits working. If I mute then unmute
the microphone in the application, the microphone
function is restored for a random interval, only to
stop again.

Wired microphone works fine with both applications on all
systems. I'm not moving around. I'm sitting within two feet
of the bluetooth USB dongle.

I did one experiment using the BT microphone as an input
to an audio capture program. I talked until I was blue(tooth)
in the face and it didn't drop out.

Google found several references to a similar problem, but no
resolution.
I have no idea how to troubleshoot this problem.
Ideas? Is there a way to tell if some other application is
taking away the microphone?
Thanks, mike