How do you ring a Swedish mobile phone that is in the UK from the UK?

The telephone country code for Norway is +47. Norway does not use area codes, per se; within Norway, you dial the full 8-digit subscriber number for all calls. In international format, you simply prefix country code +47 to the 8-digit subscriber number.

Mobile numbers in Norway generally begin with +47 4, +47 9, +47 58, or +47 59.

(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)