The scenario I described to them on a previous call was starting a business that offered a website accepting credit card payments in exchange for bitcoins. It took about an hour to explain what bitcoins were, why people would be interested in the business, and what bitcoins are used for. I agree that the reply message was vague as to the reasoning, but, I don't really care to challenge their lawyers on the matter. I really just wanted a yes or no answer. And I got it. So, if you are going to sell bitcoins for dollars -- register as a MSB. It's actually not that difficult. Being a money transmitter (different than MSB) is on a state by state basis and it seems to have a large cost of entry.