As far as i am aware you have to pay the remainder of your contract to terminate. I.e say you got 12 month left then it would be 12 x £25. When you take a contract out in uk i believe you paying for the sim service and not the phone. Phone is just a deal sweetner. Also T-Mobile can not be hold responsible if Nokia decides not to bring newest flash to their device.

I am not sure if T-Mobile is like o2 where after 9 month you can lower your tariff to the next lowest.