In my experience it has been the BB itself that causes the echo. I think that it does this because the person that you are talking to is actually hearing themselves talk originally and the natural cell delay is heard by them again as you hear it through your earpiece. Basically they are hearing themselves talk from your speaker. The reason I think this happens is because of the short length of the phone. Try turning your volume down so that the persons voice from the earpiece is not being picked up by your mic. It is a pain, but turning down the volume has worked for me, its just irritating that I have to be conscious of this with every phone call.