I am having a Nokia BH-905 and when I tried to call others using Bluetooth on a train or in a noisy environment, the other side reported that the sound was so choppy that he simply could not understand what I am speaking. However, it seems that if I use the same headset with another phone (a Blackberry Bold), there is still some choppiness but it's not as serious. However, it seems to work well (even with my N900) if I am in an indoor (or not so noisy) environment. I'm really unsure if it is a problem with my BH-905 headset or my N900...