Using your own phone in Stockholm is great, Stockholm and Sweden generally has great IT infrastructure. WiFi is abundant and 4g is just about everywhere. That said, depending on your own contract it is usually still expensive to use your phone internationally and especially surfing the web with data traffic.
Are you lucky to have a unlocked phone you can enjoy using a Swedish prepaid phone card. Below you find the details of the best offer in Sweden from Comviq. You will find it just about everywhere in all shopping spots.
Weekly unlimited calls
Package Week 45 has free calls and sms, 400 MB data included. 40 SEK extra for cheap international calls and 50 SEK for additional 1 GB data. The best price and most convinient short stay phone offer.