How much money does it cost to unlock an iPhone?

I have T-Mobile and I really want an iPhone. But, sadly T-Mobile doesn't carry the iPhone! So I was thinking about getting an iPhone from The Apple Store and bringing it to T-Mobile to unlock it! How much does it cost if I get the iPhone 4? Also, how much would it cost if i get the iPhone 4?

No money, just your soul to apple.

I don't know about 15-40$

T-Mobile actually does carry the iPhone

I can do that for you for $15 only, just drop me a message

$4.99, any model iPhone, any firmware/baseband. But it MUST be locked to AT&T initially. Once it's unlocked you may use it on T-Mobile or any GSM carrier around the world.