how is possible to Unlock an iPhone 3GS by at&t company

AT&T is the only one that can unlock

So you need to talk to them

There is nothing either Apple or the users of these forums can do to help you at all

Allan

Only the company that applied the lock can unlock it. Contact AT&T.

https://www.att.com/deviceunlock/client/en_US/termsAndCondition

Contact AT&T and request an unlock:

eligibility requirements - https://www.att.com/deviceunlock/client/en_US/?

request page - https://www.att.com/deviceunlock/client/en_US/termsAndCondition

<posting to see replies>

Then you cannot get it unlocked - AT&T's requirements are explicit on the link I posted. If you do not meet those requirements, they will not be able to unlock it for you.

Again, ONLY the carrier it is locked to can officially and permanently process an unlock for you. ANYTHING else you try is a hack, and you use those at your own risk.

Did you read his post on eligibility? Are you eligible for an unlock?

cristian25it wrote:

what you mean

Sorry cristian25it - the forum software often indicates there are replies to a thread, but the only way for me to see them is to post something to force the software to update the thread in my browser. It is a very annoying glitch in the forum software.

Then go back to what you have read and see what you can find out.

cristian25it wrote:

yes i don't have the eligibility but I've read that it's possible

Sorry, but you read bad information. If AT&T will not or cannot unlock it for you, then it cannot be unlocked (you have been reading about hacks, not a true and permanent unlock process).