I bought an iphone 5 at&t on eBay and I want to unlock it?

I heard you could call at&t and ask them to unlock it but what if I don't use them as a company? I want to use it on another carrier. Can anyone help please? Or how can I unlock it myself?

Doesn't matter… You bought it 3rd party… Call 800-331-0500, tell them you got it on ebay… And you want the subsidy device unlock code

No, it actually matters! If you are not their customer they won't unlock the phone (see the attached link) ! Do not waste the time with them. Either register an account / plan with them and then unlock your iPhone or use any of the third-party services around. Either on eBay (beware of scammers) or via the link I'm attaching. It is factory unlock, that means that your iPhone would be unlocked officially, in the Apple's databases.