Can you keep sim card from a blackberry to an iphone?

I currently have a normal sim card in a blackberry curve but want to change to a iphone 4s.
i know that the iphone sim card is much smaller but is there some way to keep the number from the bigger sim card

Ask your carrier to transfer your number to a new micro sim (Smaller something card that the iPhone uses.

Just go to your local store and they will change the sim card for you at no cost to you other than your time.

Do not bother with your phone provider, simply cut your ordinary sim card to microsim card. Google
"cut sim to microsim" if unsure how to do that. Don't worry if it does not go according to plan - you can always ask for a replacement as sim card cost virtually nothing

Cut the SIM to size. Its called a microSIM btw.

http://www.iphonehacks.com/2010/06/how-to-convert-a-mini-sim-into-a-micro-sim-for-iphone-4.html