How to get my iphone 4s unlocked?

I have a contract of a iphone 4s on orange. Me and my brother has swapped phone so now he has mine iphone and I have his android. Problem is, his android was unlocked so my orange sim works in it, my iphone wasn't unlocked so his 02 sim doesn't work as the iphone is locked to orange. How do you get it unlocked?

With a key?

Check links

Call Orange and find out if they can unlock it for free. If not, your only option to order a factory unlock code from a third party. Research which are good. I unlocked my At&t with Keys2iPhone in the past.

In which country network your iPhone 4 is locked to? You didn't mention the country name clearly. If your iPhone 4 is locked with orange Israel, get Remote unlocking method from any of the online vendors like http://www.superunlockcodes.com/apple-iphone-4/rs12wp9/ to unlock it. After unlocking your iPhone 4, you can use O@ sim card in to it.