[Priceless Luigi]

I bought an unlocked AT&T Lumia 1520 from Swappa about 2 weeks ago. I plan on using this phone for Tmobile. I used a friend's nano sim card to checked to see if it was unlocked, and it worked. Now that I have updated the phone to 8.1, would my phone be locked again?

I used the phone app to type in ##7820# to check, and it is giving me a picture of a lock and a sim card, asking me to type in the unlocked code.

UPDATE:
I switched from AT&T to T-mobile yesterday and received the unlock code for the phone from AT&T the day before. I tossed in the SIM card and found out that it is still unlocked. I also phoned ##7820# and still saw the lock and SIM icon. So the icon is a bad method to check if a phone is unlocked. Thanks everyone for their input about the situation.

[MDK22]

I think you got your answer, it's LOCKED - you have to re-enter the unlock code. If it was factory unlocked (never carrier locked) it would not require this.

I posted about this, yesterday.

[Priceless Luigi]

Thank you for the help. Man, didn't expect the phone to be relocked. Do you know ways to unlock it?
Why would it relock itself would be my main question?

[MDK22]

Thank you for the help. Man, didn't expect the phone to be relocked. Do you know ways to unlock it?

You need the unlock code from the carrier (AT&T).
Either go to the Online Unlock portal (under OLAM), but you have to be a current (or recent) customer.
Alternatively, call AT&T Customer Service (611) & talk to a CSR about your issue.

Possibly, Swappa can retrieve the unlock code from the seller.

There is also an unlock site on eBay (from Spain) which claims to unlock your Lumia 1520, though I can't recommend it.

[Priceless Luigi]

Thank you for the reply. I'm have contacted the seller on Swappa, so hopefully they respond soon. Also I'm a current AT&T customer under a family account with 3 basic phones and 1 smartphone, which was an iPhone. Do you think that AT&T would unlock my device? I looked over the Online Unlock Portal eligibility, and it seem that it could work. Sorry for asking all these questions all of a sudden.

[MDK22]

Thank you for the reply. I'm have contacted the seller on Swappa, so hopefully they respond soon. Also I'm a current AT&T customer under a family account with 3 basic phones and 1 smartphone, which was an iPhone. Do you think that AT&T would unlock my device? I looked over the Online Unlock Portal eligibility, and it seem that it could work. Sorry for asking all these questions all of a sudden.

YES, they will, as long as the device is NOT under subsidy (the seller's)

[pankaj981]

Wait a second... once unlocked a phone stays unlocked, period. If it was unlocked before then it's still unlocked

[jdandison]

I downgraded my 1520.1 to 8.0 to update to Cyan. The ATT lock certainly didn't come back. Sounds like someone sold you a locked phone.

[pankaj981]

I downgraded my 1520.1 to 8.0 to update to Cyan. The ATT lock certainly didn't come back. Sounds like someone sold you a locked phone.

Well the OP mentioned that a T-Mobile nano SIM worked before so looks like the device is unlocked. Unless the OP didn't test it correctly before

[jdandison]

I suspect OP didn't test it properly. There's no way a phone would relock itself with a retail firmware update.

[MDK22]

I bought an AT&T sim locked phone (Lumia 1520.2 RM-940), requested the unlock code from AT&T and (carrier / sim) unlocked the phone (not to be confused with factory unlocked - or NEVER carrier locked).

After downgrading to WinPhone 8.0 from Dev Preview 8.1, then installing the AT&T Cyan / 8.1 update ...
I checked the phone (##7820#) and found it was carrier locked, again. I entered the unlock code (I saved the email) and voila, unlocked, again. Just the facts, so someone else doesn't get stuck.

[MDK22]

I downgraded my 1520.1 to 8.0 to update to Cyan. The ATT lock certainly didn't come back. Sounds like someone sold you a locked phone.

Hmmmmmm, the Lumia 1520.1 you reference, is NOT an AT&T phone - it's a factory unlocked phone - a NEVER carrier locked phone. The AT&T variant is the Lumia 1520.2 (RM-940), guessing you have an RM-937 ?

When you take a carrier / retail ROM, they send the carrier software, including sim / carrier LOCK. Remember, everything is reset - if you do a factory (Hard) reset after upgrading, you don't go back to the software the device is shipped with, you go back to the latest FULL software update - TRY IT !

[jdandison]

Interesting. I've had a t-mobile SIM in my phone for months, downgraded to 8.0, installed 8.1 cyan, and my phone has been fine. Tmo SIM working the whole time. Just dialed ##7820# and it shows as locked, but my sim is fine. OP, does your tmo service not work? If it does, it probably doesn't matter what the ##7820# screen shows.

[jdandison]

Hmmmmmm, the Lumia 1520.1 you reference, is NOT an AT&T phone - it's a factory unlocked phone - a NEVER carrier locked phone. The AT&T variant is the Lumia 1520.2 (RM-940), guessing you have an RM-937 ?

Correct, apologies, I have thr ATT variant.

[MDK22]

Interesting. I've had a t-mobile SIM in my phone for months, downgraded to 8.0, installed 8.1 cyan, and my phone has been fine. Tmo SIM working the whole time. Just dialed ##7820# and it shows as locked, but my sim is fine. OP, does your tmo service not work? If it does, it probably doesn't matter what the ##7820# screen shows.

Was the sim in the phone, when you took the update ?

That could be the difference, but as you said - interesting !

better safe, than sorry

[Priceless Luigi]

I got the phone when it was just windows phone 8. First thing i did with it is I factory restored it and then used a friend's Tmobile sim card and it worked. I can make calls, send and receive texts, browse the web, etc. Since then I assumed it was unlocked. Then I updated the phone to 8.1 when AT&T announced it earlier this week. Today I checked the ##7820# and it said it's still locked. Not too sure what is happening. U'm going to Tmobile this Friday to check if their sim card still works

[sstiwari]

I bought an unlocked AT&T Lumia 1520 from Swappa about 2 weeks ago. I plan on using this phone for Tmobile. I used a friend's nano sim card to checked to see if it was unlocked, and it worked. Now that I have updated the phone to 8.1, would my phone be locked again?

I used the phone app to type in ##7820# to check, and it is giving me a picture of a lock and a sim card, asking me to type in the unlocked code.

I also have an unlocked AT&T RM-940 in India. It also shows lock & sim on typing ##7820#, after cyan update.

However, tried four different Indian Sim-cards and there is no issue at all. The Phone remains unlocked. So do not worry about lock image. Actually insert another sim card and check network services. A Nokia phone once unlocked is always unlocked, even Nokia can not lock it again.

Cheers,

[Priceless Luigi]

That's what I assuming. I'm currently on AT&T at the moment, but will be going to T-mobile on Friday to switch. I have no access to a T-Mobile sim card at this moment.

[Priceless Luigi]

Well the OP mentioned that a T-Mobile nano SIM worked before so looks like the device is unlocked. Unless the OP didn't test it correctly before

I was able to make, and receive calls, send and receive texts, browse the web with LTE, and etc. In addition, the phone app said T-mobile on the live tile. Not to sure what is happening. I going to T-mobile on Friday to check it out.

[black_lion]

Mine is definitely still unlocked (completely functional)but asks for the unlock code when I dial ##7820#.

[foxbat121]

It just shows you that dial ##7820# is not a reliable way to test if a phone is SIM locked or not. I have never heard any GSM phone get re-locked after a firmware update.

[Priceless Luigi]

It just shows you that dial ##7820# is not a reliable way to test if a phone is SIM locked or not. I have never heard any GSM phone get re-locked after a firmware update.

Do you know any cases where the phone was relocked?

[pankaj981]

Do you know any cases where the phone was relocked?

That really doesn't happen

[MDK22]

It appears I stand corrected, wish I had a T-Mob sim to test it.
I will check my wife's (my old L920) phone after her Cyan update, her sister has T-Mob (& the right size sim). I unlocked it before I gave it to her, still have the unlock code.

BTW - I offered her a choice - L1520 or another L920 ... she said ' ... if you want the BIG phone, get it, just hand over yours.'
Only one of the reasons I love her !

[badr0b0t]

Why don't you just pop in a nano sim to answer your own question? Nano sim is just $7.50.