WE CANNOT UNLOCK THIS DEVICE FOR YOU BECAUSE WE DIDNT SELL OR ACTIVATE IT

Hello minhLC93VN, we're here to help get your device unlocked.

As the ACEs @dwill05 and @formerlyknownas  mentioned, you would want to have your sister contact AT&T to request the unlocking of the device. The device would need to meet all unlock eligibility requirements.

• Is an AT&T device and isn’t active on another AT&T account.
• Was paid in full when you bought it (not on an installment plan). You won’t have to wait 60 days to unlock it.
• Has a paid-off installment plan.
  • Paid through your monthly bill: Submit your unlock request at the start of your next bill period.
  • Paid off early: The wireless number assigned to the device must be active for at least 60 days. Wait 48 hours after you make your final payment to submit your unlock request. 
• Doesn’t have a past-due account balance. Make a payment to bring your account current. It will take 24 hours for your payment to post. 
• Hasn’t been reported as lost, stolen, or involved with fraud.
• Is an AT&T PREPAID phone that has had paid service for at least six months.

Let us know if this helps.

Jeff, AT&T Community Specialist

Have you talked to your sister - she's the one who gave you the phone?

Either she did not use it on AT&T. It's been replaced by warranty or insurance. Or it is not locked to AT&T even though she may have used it on AT&T.

In any of these cases, AT&T is not going to unlock it for you outside of the USA. If your sister is in the USA have her do the unlock which she should have done before giving you the phone

That message means that the IMEI of the phone isn’t registered in the AT&T unlocking database.  The only way to solve it is to call them and try to get the IMEI added, or request that they manually approve an unlock.

Hi @dwill05 , You're right. Which the phone# I should call? I'm living out side of US and not familiar which correct phone# can support like your suggestion. Have tried some phone# but can not be successfully.  Thank you

The international customer service number is +1.314.925.6925

I agree with the other suggestion on having your sister do it if she’s the one who bought it.

There is no point calling that international number because it is for AT&T customers who are traveling outside the United states. They're going to ask which number you're calling about and you don't have one. Please have your sister unlock the phone with her information from inside the USA. Even if she is a foreign customer at least her phone calls won't cost her $3 a minute for long distance.