Thank you for your responses!!! I've already known the differences between this 2 units, however, it seems that one missed me completely. Correct me if I'm wrong, but NH900 can operate both on gumstick battery and with AA using attachment. And RH910 doesn't have an attachement for the AA battery and can operate only using gumstick battery. Considering the prices, I know that they are high (here in Canada), but that's the fact of life here. (and you have to add 15% of GST + PST on that price). The difference between Canadian and US is not big enough, because of s&h expences. For the microphone, I'll try to search the forum more! Thank you once more, Sincerely yours Bojan