I have problems with the quality of reception on my IP phone. My correpondents can hear me clear, but most of the time, I can't hear them clear. It is like if there were missing packets. Here is the setup: router zyxel prestige 600 series, IP phone Grandstream Budge Tone -100, VOIP provider Iconnecthere, ADSL boradband (speed varies from 500 to1,500 kbps). Can anyone help?