Phone dialer in WinXP

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I can dial the number, and can hear the other side, but the other side
can't hear me, nor can I dial extra numbers once the call starts,
(extensions, menu options etc.).

I am using the Logitech headset which was tested and works fine, audio
is set to headset's microphone, and I tried using the small dial pad
from the call window, but i does not work.

Could someone tell me what the problem is?

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