IPhone 5 how to buy it locked?

Hi. I'm a non-USA based customer. I want to buy iPhone 5 with AT&T. But I don want to use it with AT&T. I will go for a third party unlock…
If I get it from a friend on his account paying 300$ and I take the phone from him then How much will he be penalised?

If he bought it on contract he'll still be obligated to pay for the phone/plan until his contract is up.

Also there's no say whether the iPhone 5 will be unlockable from the get-go with third party methods.