EU-based mobile accounts are exempt from roaming charges, including for data. But those with non-EU mobiles who want to make or receive domestic calls, get in touch with family back home in a non-Skype kind of way or check their Instagram every 5 seconds can buy one of the many inexpensive, prepaid starter packages on the market. These will give you instant access on a pay-as-you-go basis. The kits are available in most supermarkets, R-Kiosks, Statoil fuelling stations, the post office and from the service providers themselves, and can be topped-up online or at the point of purchase. See providers' websites for further information, data prices, etc.: Elisa, Telia, DIIL, Tele2.