Call customer service and if they can help you, they will. I've switched phone numbers to different SIMs several times and almost every operator was very helpful. I got a blockhead on the other end one time and I just said thank you, hung up, called right back and got someone who could take care of it. They always tell you it's going to take a few hours for the change to take effect but for me it's always been near-instantaneous.

Might be a different story with pre-paid so just give a call.

Congrats to the new members of the N9 Club. Agreed, it's the way a touch screen phone should work. Everyone that sees my N9 is blown away at the quality and simplicity.