Supreme Roastworks is a decent café in this town which has amazing baristas and hand brew. Seating is a bit limited although, but you can grab a place and catch up with your work using their free Wi-Fi.
Oslo Central Station- you can get a prepaid sim card from a NetCom store, its located near the exit to Karl Johan on left side.
Mesh is the first coworking space in Oslo and also the best one. Its very well equipped and has everything a nomad needs. They also have a ping pong table for your free time. The internet is pretty good with speed up to 20mbps.
“Mesh” is a good place/caffe to work in Oslo. Other coworking spaces are: TSV (Tøyen startup village) and Spaces.