Do I need to buy a new sim card for an iphone 5

I currently have a blackberry but have brought an iphone 5 off of ebay and I'm wondering wether I need to get a new sim card to go in the iphone? If I do need a new sim card, will I be able to keep my current number? And I'm on a sim only contract, will I be able to stay on that? Hope you can help, thank you!

Added (1). The sim I currently have is vodaphone and the iphone 5 is also on vodaphone

You could cut your SIM to size or have your carrier issue you a nanoSIM with your number on it.

You need sim cards like 3G, Vodafone, O2, Orange. If your iphone 5 is unlocked then all the sim cards will work if not you have to use sims like above. You need micro sim card for iphone 5 which is smaller then standard.