I know this is thread is regarding a 925, but I thought I'd share my experience with you. I bought a 920 off eBay. First, I tried the chat from the international page and told them I was traveling, they said they could unlock it and then came back and said they couldn't because it was still active on an account, they told me to call customer service. I called AT&T and told them that I bought it off eBay and it was supposed to be unlocked, they checked the lists to make sure it was not lost or stolen and unlocked it for me, he even walked me through unlocking the phone. This was about 2 or 3 months ago.
I've also read that you can have someone that has an AT&T account call and get up to 5 phones unlocked per year as long as their account is in good standing. There is also a web form for this.
Unlock your AT&T wireless phone or tablet- AT&T Wireless Support
Good Luck!