Renting phones is certainly not a "normal" thing to do, and if at all possible, will be expensive.
If you have unlocked GSM phones, it will be way cheaper to bring your own phone, and buy a prepaid SIM card. Heck, even buying a new phone with a prepaid card would be cheaper. You can buy prepaid SIM cards in any kiosk or gas station, and even mot convenience stores, and there are small booths selling phones and prepaid cards all over the place. The smallest prepaid cards are usually NOK 150, and filling up more is very easy. (NOK 150 on a prepaid card is approx 200min in to Norwegian phones or 25min to USA from any provider.)
Do note, that since a few years ago there is mandatory registration when buying a SIM card. You will need to show IDs, and some places like convenience stores might be reluctant to sell to foreigners.