Interesting enough these two operators have previously not cooperated together in their network building, instead there has been two blocks with 3 and Telenor on one side for the UMTS and Telia + Tele2 on the other side. But since Telia is building their own network and the operator 3 decided to stick with UMTS for the time being the left over operators Tele2 and Telenor have decided to form a new partnership.
I find this really interesting and I think it will be a good thing for the customers pricewise in the end since competition will start on several fronts at the same time. The differences between one operator and another will probably become more and more blurry as these cooperations proceeds.