Can you switch sim cards between iphones and blackberry?

My blackberry just completely died on my screen won't even turn on. My cousin from France offered to let me use her iphone 4 while she is here for the next month and a bit. Can I just switch my sim card and put it into her iphone? Do I have to tell my carrier (telus)? Is there any other options?

If they sim card fits then yes and if not you can take it to your carriers store and they can get a sim card that will fit in it

The 4 uses a micro sim. Not sure about the size of your BB. Problem is her phone is likely locked to her home carrier network so during an activation of the 4 by you, after you have installed your sim card, you might get the error if her carrier and your's are different. If the phone is unlocked, no problem. Best luck.

Yes you could but there are some considerations in mind

1. Size of SIM. BlackBerry likely has a miniSIM but the iPhone 4 uses microSIMs. You'd have to cut the SIM to size in order to work in the iPhone.
2. Unlocked or not. If the BlackBerry was on a different carrier than the iPhone then the SIM wouldn't work. The iPhone would have to be unlocked.