Would i be able to trade my droid for an iphone?

I have a droid right now and I'm on a contract and I used my upgrade to get this phone. My friend wants to trade her iPhone 4s for my droid RAZR m.Am. I allowed to do this and then replace the phone I have now for an iPhone on the contract or will they not let me since I'm on a contract and used my upgrade? There's nothing wrong with wither of the phones. We just don't like our phones now and I want an iPhone and she wants a droid.

If you're sim cards are excepted in both the phones i.e. Interchangeable then there's no problem at all and you can safely swap the phones with each other.