SlackerLX, thanks for the reply. I haven't tried your suggestion yet. But, I finally seem to got it fixed (I think) with master volume control itself. In the capture tab of Master volume control, we have microphone control and under that we have a "capture" and "toggle" (or something like that - I don't have my ubuntu in front of me now) icons. I turned off the "capture" icon and that seems to have fixed the problem. I don't know if this is a permanent fix or a fix for this problem at all - but now everything seems to be working fine and am able to make VOIP calls.