The process of applying for a Norwegian fødselsnummer can take quite a while. At the same time, everything in Norway is paid by credit card which you cannot get without a bank account which in return requires the fødselsnummer. Are there any possibilities of getting a Norwegian bank account prior to receiving a fødselsnummer?
It should be possible to open a Norwegian bank account using a D-number. This is basically a temporary (dummy) ID number for foreigners. There may be other requirements such as country of residence and (large) minimum deposit.
Of course, it takes time to apply for this so if you plan to stay more than six months, you may as well apply for the real ID number (if applicable).