Yes. Just go to an Apple store and get a microSIM for free or go buy one at a Fido kiosk for $10. Then you can either use the My Account page on fido.ca to move your line to the microSIM or you can call 611 and have them do it for you.
One thing to keep in mind is that if you are using a BB, you probably have a fairly small data plan. If so you will want to be careful with your data usage on the iP4.