Hi Julia, Great to hear you are cycling in Norway for 3 months!

There are 2 sim cards I recommend with the best coverage.

You require a passport to purchase one (which obviously you have). You will find every large town will have a Telenor or Telia store and I think you can buy them at local kiosks such as 7/11.

Telenor Norway: 49 NOK
Telia Norway: 429 NOK or 99 NOK

https://www.telenor.no/telenorbutikken/
https://www.telia.no/kundeservice/butikker-og-forhandlere/?filter=offersMobileHelp&q=oslo&lngMin=10.208334273437497&lngMax=11.361898726562497&latMin=59.79047399542177&latMax=59.997127836594274

A lot of great info here in English about prices and packages: https://www.traveltomtom.net/destinations/europe/norway/prepaid-sim-card-norway