How can I get rid of the echo that the person on the other end complains about?
Turn down your phone volume. Acoustic feedback from the speaker to the microphone of a telephone handset or computer can cause echo.
I tried several suggestions, but still hear echo, what can be the cause?
In some cases, especially during periods where echo is present when none existed before, it can be due to network (WAN) connections and/or your carrier. In these cases the echo will most likely be short lived (days). In some cases, where you hear echo more often when you call specific people, (most likely local) this can be because the local phone carrier is not using proper echo cancellation techniques and the result will magnify echo with VoIP calls. Baring the aforementioned cases some echo can be caused by faulty or corroded wiring.