How to unlock an iphone 4 att to tmobile?

I just bought an iphone that only works for att. What's a free way to unlock it at home?

Not gonna' happen.

No free way to unlock it. You have to buy the inlocking code… Which depends on the phone it. I bought the code online… And put in all my phone info. So the phone actually unlocks itself after 2 days. The cost of mine was about $25.or, you can always have someone unlock it for you. But it will be way more expensive.

3 ways of unlocking, only 2 free ways.

1) have somebody with AT&T call and ask for an unlock code - this is hit or miss.
2) see if you can unlock it yourself, use this wizard, enter in phone, baseband version, and see what it says: http://www.iclarified.com/wizards/index.php

now if neither of the two above are an option then your only option is to pay a service to get you the unlock code.

with any other phone this would typically cost you only about $10-15 but with an iphone's, people who unlock it realize that users of iphones are used to paying a lot of money.

its highly unlikely to be able to find somebody to unlock it for under $50, and most likely a little more.

i can personally recommend http://www.cellunlocker.net/, i have used them at least 20 times without problems.

There's a software unlock available for the iPhone 4 but requires you to be so a specific baseband and software unlocks are usually a bit unstable. But its worth a shot if you are looking for the unluck instructions see the source website.

The free way is to jailbreak your. This requires a bit of research on google, took me about 2 hours, but it worked for me. Problem is, every time your phone updates ect. It reverts back to before.
http://www.iphonehacks.com/jailbreak

I ended up accepting that I'm going to have to get it done professionally (legitimately) and used unlockiphoneonline.net haven't had any problems since.