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I have an ongoing problem with using an overseas carrier's sim card in my Samsung S10 Plus phone. I got this phone in May 2019 after committing myself to Vodafone's 24-month contract. I am in the United States for work and want to use the local carrier T-Mobile to save on overseas roaming charges from Vodafone. I was told by Vodafone once the Network Unlocked Code (NUC) is inserted, it will allow Vodafone mobile service subscribers to use other carriers overseas. To my dismay, this is not the case at all. Not expecting my phone will be locked up by Vodafone, I spent 105 USD for the T-Mobile sim cards. My phone couldn't read the overseas sim cards at all.
Heeding the advice from Vodafone, I obtained the Network Unlocked Code (NUC) from Vodafone, but the NUC failed to unlock my phone despite confirming with the Vodafone Helpline Representatives for more than 6 times. T-Mobile has tried 10 different sim cards with me, but my phone cannot recognize any of them because the phone just simply cannot detect the cards. None of them. The identical cards were inserted in other trial phones from T-Mobile and my son's phone which he didn't purchase from Vodafone. All these phones worked seamlessly. Vodafone representatives said the lockup was a problem caused by the T-Mobile network. However, how could this be a problem from T-Mobile if the sim cards work for every single phone except my contract phone locked up by Vodafone?
The worst part is that Vodafone has no control in ensuring that the NUC will work for every subscriber who wants the option of using overseas carriers instead of paying the expensive roaming charges as I do reluctantly. I have paid for the T-Mobile sim cards as Vodafone representatives promised me the NUC will unlock my phone for overseas carriers. Now, I am stranded. It's double jeopardy. On top of the 6 pounds roaming charges per day, I've paid 105 USD for the sim cards that can't be used on my phone because it is locked up by Vodafone. Another concern is that once my contract with Vodafone ends, my Samsung S10 Plus will be useless because I can't use it for other UK carriers unless I stay with Vodafone.
The fact of the matter is that Vodafone should have advised you that they cannot guarantee that a Nuc will work when the phone isn't in the UK and an alternative UK activated sim card is used to complete the process @MingTam
The iPhone being the only exception as they are not unlocked by a Nuc but instead are unlocked centrally by Apple.
As I see things your options are ~
Send it to someone you know in the UK and they unlock it and then send it back to you.
Or try a local Highstreet Store that advertises they unlock phones. Of course I understand that would come at a cost.
Don't use online unlocking sites is.my advice as they can go wrong and acquiring a refund is hard.
Or buy a sim free phone and use your sim card of choice and sell the phone that is locked to Vodafone.
Current Phone > Samsung Note 10+ 5G _256Gb > Model: SM-N976B.
Samsung One Ui 2.1 / Android 10.
Samsung Gear s3 Frontier Watch.
Samsung Galaxy Buds.