Problem:

The customer hears echo during calls. 

Solution:

In a voice call, an echo occurs when you hear your own voice repeated. There are 2 ways echo can occur:
1. Electronically through poor cabling or latency. Review/replace cabling or address the latency issues.
2. Acoustic feedback through sound waves between speakers & microphones. Ask the other side to lower the volume to reduce feedback.

Note: Hands-free speakers & conference calls are especially sensitive to echo. It is suggested to mute when not talking when on a conference call.