[Windows Central Question]

I have a valid AT&T unlock code for my device. I have entered the code via using another SIM card and the ##7820#.When the SIM card is inserted (Walmart Family Mobile T-Mobile towers) the message "SIM ERROR" is displayed. I tried a 2nd WFM SIM card, same issue. I discovered the ##7820# with no SIM card inserted and when I enter my 20-digit code, the locked symbol shakes back and forth. I cannot get the code to work. AT&T customer service guarantees the code with my IMEI number and won't issue another code as the code provided is unique to my IMEI number.

[fitchalcyone]

From my experience, I've unlocked four Lumia phones with AT&T. Each time I've just done it without a foreign sim card inserted and via the ##7820# without any issues whatsoever. I hope you are able to get this resolved somehow. Have they verified with you that they have the correct IMEI number on their end?

[L Beezy]

Bear in mind that you only have 3 attempts to correctly enter the unlock code before your phone is permanently locked to the AT&T network. Hopefully, you haven't attempted 3 times...

[PaulFSemicolen01]

they have confirmed verbally they have the correct IMEI number and the unlock code they gave me is tied to that number.

[PaulFSemicolen01]

when the new sim card is inserted it says I have 10 attempts. When I tried the ##7820# way, there is no "attempt counter" and I have entered the code correctly, check and rechecked before pressing the check mark to attempt the phone unlock. the previous owner is my coworker, and he bought the phone new and has always been an AT&T customer. (Just a little further info in case there were questions). Does the lock shaking when the code is entered imply an invalid code or permanent lock of the device?

[PaulFSemicolen01]

okay, now something weird happened. I turned my device on and dialed ##7820# to show my coworker my issue, and the phone showed it was unlocked! Great! So i put the sim card in and reset the phone. However, the prompt for unlocking the phone popped up again. when I reenter the code it still says "SIM ERROR".... WTF!?!?!?!

[tai4de2]

Sounds like maybe the SIM card itself went bad, I've had that happen. Does it work in another phone?

[PaulFSemicolen01]

One thing we are thinking might be causing the issues. I upgraded the the phone to Windows 8.1 developer preview. I will download the Nokia Lumia recovery tool and factory reset back to Windows 8.0 and start the whole process over again...

[PaulFSemicolen01]

Sounds like maybe the SIM card itself went bad, I've had that happen. Does it work in another phone?

I continue to use the SIM card on my Walmart Family Mobile phone as it stands until I can get the Nokia 920 Unlocked. I tried another WFM SIM yesterday with the same results

[MDK22]

Bear in mind that you only have 3 attempts to correctly enter the unlock code before your phone is permanently locked to the AT&T network. Hopefully, you haven't attempted 3 times...

The OP is correct - you have 10 attempts before the phone is permanently LOCKED. Use them wisely ...
I assume you wiped the phone, originally, to enter your account - IF not, did the previous owner have a sim password set?

[PaulFSemicolen01]

The OP is correct - you have 10 attempts before the phone is permanently LOCKED. Use them wisely ...
I assume you wiped the phone, originally, to enter your account - IF not, did the previous owner have a sim password set?

Correct the phone was completely wiped before i got it. Following me acquiring it before I received an unlock code, I decided to set it up in wifi mode the way I wanted it to prepare for the long wait from AT&T. my coworker and I think the developer preview 8.1 may be messing with the process. I am going to try to factory reset it back to 8.0 when I get home from work tonight.

[fitchalcyone]

I unlocked my yellow 1520 during a point when I installed Developers Preview on it. Then, when I sold it to a friend, I used the Software Recovery Tool to bring it back to 8.0 as he wouldn't be familiar with the side updates. This locked the phone again, but the old code still worked and unlocked the phone just fine.

[MDK22]

I unlocked my yellow 1520 during a point when I installed Developers Preview on it. Then, when I sold it to a friend, I used the Software Recovery Tool to bring it back to 8.0 as he wouldn't be familiar with the side updates. This locked the phone again, but the old code still worked and unlocked the phone just fine.

^^^ VERY IMPORTANT ^^^ so make sure you save the code, somewhere. Check after phone updates, also.

[MDK22]

Correct the phone was completely wiped before i got it. Following me acquiring it before I received an unlock code, I decided to set it up in wifi mode the way I wanted it to prepare for the long wait from AT&T. my coworker and I think the developer preview 8.1 may be messing with the process. I am going to try to factory reset it back to 8.0 when I get home from work tonight. then unlock, then upgrade to Dev Preview, then check for unlock (if needed)

RED comments

[MDK22]

Bear in mind that you only have 3 attempts to correctly enter the unlock code before your phone is permanently locked to the AT&T network. Hopefully, you haven't attempted 3 times...

Sorry, Beezy, you're thinking about Phone sim Password ...

MODS - who picked this as Best Answer, it's not even correct.