The issue is that there are many possible causes for echo over VoIP. It may take some trial and error to identify the exact cause of the problem.
Here are some possible causes:
1) Echo Cancellation turned off
- Express Talk has a built-in Echo Cancellation algorithm to help suppress some of the unwanted effects of Echoing. You can turn it on by selecting 'Use microphone and speaker and turn echo cancellation on' from the Communication Device selection under options.
2) Poor Network connectivity
- Run the Network Setup Wizard in Express Talk to help solve network issues and ensure that there is no Firewall or router which is blocking ports that Express Talk is trying to use (by default Express Talk uses UDP 5060 and UDP 8000-16000 last time I checked). Regardless of whether this is causing echo or not, it is important to make sure there is a clear network path for Express Talk or you may encounter several other problems.
3) Feedback Loop
- If you are talking to callers on speaker-phone, it is possible their voice is being sent back through the mic which can cause feedback. My understanding is that because VoIP has a larger latency (or delay) than its landline counterpart, this feedback is perceived as an echo.
Edit: another one
4) The Service Provider
- I have used some VoIP service providers before that had terrible problems with echoing, I eventually had to drop them as a carrier. It is possible the problem may reside on the service end.