Hi,
First of all, check if your main WAN is set to mobile.
Second, you can try setting your APN to AUTO and see if the router gets a data connection even without public IP.
Lastly, make sure that the other device gets a data connection once you put Telenor.se SIM in and insert a custom APN (You could use your phone to check that). If it doesn't then it might be the issue with your operator, maybe they didn't activate you the service, that you could use their Public IP APN.
EB.
