Answer to: How do I unlock iPhone 3GS?I did my iphone factory unlock at Jailbreakhome.com. I can use my phone now to any carriers.
Answer to: How to unlock iPhone4You can iphone factory unlock your phone by following the process here. They did it remotely. 100% working.
Answer to: How do I factory unlock my iPhone for free?I don't think there is an iphone factory unlock service for free. But you can check Google maybe you can find a process there. But I really suggest you to have it taken care of by a professional to avoid issues.