Can any lock iPhone 4s can they be unlock able?

I want to buy a iPhone 4s on eBay but some are not unlocked and I wanted to know if a AT&T iPhone 4s be unlock so I can connected to t mobile with the gevey card?

Yes If you dislike the idea of connecting your iphone 4s to a computer every time it freezes or needs to be rebooted, then consider using http://attiphoneunlocker.com/ to allow your device to boot without the need for it to be tethered to a computer. A gevey sim is a hardware 'hack' which tricks the iPhone into making a call via a different route. You will never be able to update your handset if you use a Gevey Sim. Because they sit 'behind' your own sim, they are also prone to getting stuck into the iPhone forcing a trip to an Apple Store to take the phone apart and get it removed, which they now refuse to do and claim they void the warranty.It's totally unsupported by Apple. Our method turns your iPhone into a factory unlocked unit, meaning you can always update to the latest version of iOS. Your iPhone is an expensive device, and you want to keep up with iOS updates as Apple brings out new features etc.http://attiphoneunlocker.com/faq/

Only the service provider can unlock 4s.