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I recently flashed a custom ROM on my Samsung I9300. Everything is working fine, except I have to enter a 'SIM network unlock PIN'. I assume, that this is not the usual 4-digit PIN code. If I enter the correlating correct 4-digit PIN, it says 'SIM Network unlock request unsuccessful'.

  • I tried different SIMs from different providers which are working in a different mobile phone.
  • The problem appears with Slim 5.1.1 and 4.4.4, CM12.1 and OmniROM 5.1.

My phone was running stock firmware Android 4.3 and I never had this problem (even if I once changed my provider). There are plenty of tutorials about how to unlock the I9300, but none worked so far, there are also many non-free services for unlocking which seems rather untrustworthy to me. It would be new to me, if the phone is or was ever branded.

There is the possibility to unlock the phone by using the service menu by entering the secret/hidden code

  • ##197328640##

like shown in this tutorial: https://www.youtube.com/watch?v=f1hzeBEeO_k. Why is the code (or others) in Slim not working?

Could you please verify too that the only possibility to unlock the SIM is to buy a specific unlock code?

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    The video you've posted was of someone taking advantage of a software vulnerability in the stock TouchWiz-skinned Android 4.1.1 for the S3 - it was patched soon after. Upgrading the software after the unlock seemed to work, but no idea how it will work with flashing a new ROM. – ZeroPaladn Jul 20 '15 at 12:34
  • Okay, thanks for the comment, I didn't know. I just watched to video until I realised being unable to use the code. If so, it is useless and I will remove it from my original post. Where do you know from? – de-facto Jul 21 '15 at 6:03
  • I had used the vulnerability several times with previous devices to get network unlocks. Samsung smartened up fast with that and patched it in their OTA updates to 4.1.2 or 4.1.3. – ZeroPaladn Jul 21 '15 at 12:19
  • I understand. What happened when you flashed a newer (custom) ROM, did you have to unlock again? If not, what do you think about the possibility of flashing an old vulnerable stock ROM, unlocking it and later using an actual ROM? I'm not sure yet what I'll do. Maybe I go to a local handy shop to get it unlocked, there I have to pay some Euros too, but at least I have the security that it works. As far as I found out they are cashing 15 - 40 €s for that, which is ridiculous much. – de-facto Jul 24 '15 at 5:14
  • The device was "retired" suddenly (I dropped it and broke it) so I couldn't tell you if the network unlock persisted through a ROM flash. I do hope someone can offer more insight to this. – ZeroPaladn Jul 24 '15 at 12:21
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I got the phone unlocked at a local mobile phone dealer for € 20. This worked.

Generally I'd say it is interesting how this network SIM lock comes from, because my phone never has been locked or branded by a provider. The stock firmware worked with different providers. The problem only appeared for the custom ROMs.

And be aware when changing your SIM card! I broke mine 2-times only by exchanging it (probably scratching the chip's surface) and had to buy a new one and get the old number transferred to the new.

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