the S II has TWO MICROPHONES. Yes, the phone has one microphone on the top, right to the headphone plug and one on the bottom, right to the usb plug.
Most voip clients are using by default the wrong upper microphone. So raising the microphone gain is just a workaround for this issue.
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.