I know the phone is unlocked when paid in full from Apple, but what about if you need to get a replacement later on down the road? Is there a chance an unlocked phone could be replaced with a locked one by the Genius Bar? Would it be in the system as the carrier's phone or a plain unlocked model? I ask because all they had left was the Sprint model. I bought it full price, it's unlocked, but I'm on the fence about exchanging it because I don't want Sprint to have any power over my phone.