Can I switch my sim card from Blackberry to Iphone?

Ok so I've had a blackberry for the past 2 years and the track pad on it recently stopped working. I'm on a 3 year plan with bell. My girlfriend got an Iphone 5 last weekend and she just gave me her Iphone 4. She told me I can simply take my blackberry sim card and put it into the IPhone. Is this compatible? Getting the phone from her on tuesday so please let me know if it's possible.

Nope

Yes you can. Search google - how to cut your sim.