If you're hearing your own voice back
1) Try turning down the mic volume
2) Try playing around with the listening volumes. If it's all the way up on the phone, try turning it down on the headset (try it the other way too)
3) We could also try getting the volume at about halfway on the phone and halfway on the headset
If the person on the other end is hearing the echo
1) Check compat (usually 1, located underneath the charging base)
2) Try turning down your listening volume using the buttons on the headsets. With the LH270 and LH275 especially, the microphone can pick up telephone conversation from the ear speakers if the volume is too high!