Problem Verifying Norwegian Land Line

I've been trying to register a land line telephone number in Northern Norway with Rebel so that I can use it to make and receive calls via Rebtel (the mobile signal here is very poor). The land line here belongs to a friend and is used for internet (dial-up - no broadband here yet) as well as phone calls so I'm not sure if that might be part of the problem or not. Have tried myself from here using Rebtel's web page and also asked friends to try while the line is not in use but verification of the line always fails. Do you have any advice? Rebtel is working fine through my mobile when I can get a signal.