Can i get a replacement sim card with my iphone contract but to go in a normal phone?

I currently have a iphone and my mum has a blackberry and her contract is due to renewal
so i'm going to get a new iphone and she wants to keep the blackberry
so i was thinking of telling my phone company i have lost my phone and get a replacement sim so she can have it in her blackberry because i can't just take the one out of my current iphone and put it in the blackberry its a different size
so we end up swapping contracts where i have a new iphone on her contract and she has the old blackberry on my old contract and a iphone to sell… Does this work?

and also does a iphone 5 sim work in a iphone 4?

thanks for your help if you managed to get your head round it!

Since iphone 5 use a nano sim card, it is smaller than the micro sim on iphone 4. But you can use an adapter, which will make it easy to fit. Please see the source for your reference.