Can you switch out sym cards in iphones?

I want to have an iphone on virgin mobile. But the iphones for them are super expensive. I was wondering if i get an iphone for at&t could i switch sim cards and make it a virgin mobile iphone?

This is possible BUT you need to find out from at&t if their phones are locked to their networks only! Even if it is locked you could have the iphone unlocked by taking it to an phone specialist

NO! This is NOT possbile.

I guarantee it.

The ONLY phones allowed on Virgin Mobile USA's network are Virgin Mobile USA phones.

ONLY Virgin Mobile USA iPhones can work on their network. I guarantee it!

Looks like you'll be paying full price if you want an iPhone on Virgin Mobile USA.