When Telenor were privatised the license required them to sell capacity at cost to other operators. The same license requirements hold for mobile towers so all the small operators can piggyback on their infrastructure at cost. The result is that we have over 50 operators competing on services and add-ons while having approximately the same base network quality.
This is largely the case for ISPs too and it works great I think.
what kind of services or add ons would you possibly want with a cellphone? most of the "features" they offer around here are things I'd pay money to not get. I mean, I guess tethering, but I personally am a little bit offended I have to pay extra for that rather than just paying for the data (I do pay extra for tethering, because if you want the good network, that's another fee you have to pay if you are being honest and don't want to spend a bunch of extra time sysadmining your phone)