I admire your valiant attitude, and your courage. Norway is a particularly difficult jurisdiction for this kind of activity, and taking into account the small potential customer-base (albeit larger now that you accept foreign customers) I imagine you are, to a large degree, ideologically motivated.
Even if bitcoins were liable to sales tax in Norway, we do not sell bitcoins. We are an exchange. A more relevant question for us would be whether our commission is tax liable or not.
There is no doubt that the commission is subject to sales tax. And even if you are not selling bitcoins, you may still be held responsible to a certain degree.
I think Norwegian legislation is a bit of a double-edged sword for bitcoin. Either it will be considered a currency/financial product and sales tax does not apply, but in that case all the legislation that regulates financial products applies to it. Or it will be considered a regular product, in which case sales tax must be applied, but a whole lot of other onerous legislation does not apply.
I hope you issue an update when there is more clarity around the question.
Best of luck!