i was in the same boat as you stef ....you need to have some kind of sim though from vodaphone but registered.
I brought the n95 8gb ....looked on the net for a unlock ....found the safest way to be vodaphone...they are £20 to unlock if you not got a sim that is registered. you then just pop in the sim card and put in the code they tell u then it unlocked.
Btw stick the garmin sat nav on it ....its gr8
...think its in the downloads if you aint already got it..