Nokia has had a great OS for years, but the Maemo engineers haven't been allowed to put a radio in their devices until the N900. Now they can.
Keeping phone and provider separate is great for the consumer, but not in the long run since the phone companies don't get the market they need.
i.e. it would be great if I could use the iPhone on any network I wanted, but without an exclusive deal with AT&T, Apple wouldn't have made the kind of cash it needs to be truly profitable and stay at the top of the market.
Nokia pandered to cell companies for too long, but then went in the exact opposite direction and lost a huge chunk of the US market with them....