[Q] Echo on VOIP topic

I have a Nexus 4. The main VOIP I use is Comcast's Voice 2GO, but I also have tried others. The common denominator is the caller on the other side always complains about echo of his own voice.. It doesn't seem to matter how I am using the N4, no speaker, speaker, bluetooth hand free headphone. No matter what I try they complain about echo. On my side it sounds

Any way to avoid the echo?