old SIM cards it may be necessary to replace it with a newer SIM. I did this when I tried to use my SIM card from a 7230 with my newer, more modern 8300. Couldn't get my Blackberry Web Browser to appear. I walked into a T-Mobile store and just asked. They set up a new SIM card for me in about 5 minutes, free of charge.
Now this could all have been because I was trying to ge the original Curve to work on T-Mobile way before it was supported. I had an unlocked Rogers Curve, the OS from O2 of the U.K., and T-Mobile service. But the bottom line is that I kept my old number and got the new SIM for free.