Using laptop headset for T68i via bluetooth

Why can I only speak with myself?

I have a USB headset w/mic (from Labtec) connected to my PC.
The PC also has a USB bluetooth stick (Trust BT120).

The PC and my T68i are paired. The PC is the first item in the T68i
pair-list.

When I make a call with the T68i it makes a Bluetooth-connection to
the laptop; but the only sound I can hear in the headset is my own
voice is received from the T68i built-in microphone. First of all,
this mic should be shut off -- secondly the mic in the headset should
be active and transfer my voice to the person at the other end.

Can anybody help me figure out why? - so that I can use my pc/usb
headset for the T68i.

Thanks in advance!
/Thomas.