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I have an iPhone 4S from Verizon, which they've "unlocked" for international use. I say "unlocked" in quotes because it's still restricted from US SIM cards. I'm able to use any international SIM, but I can't use a SIM from AT&T, T-Mobile or AirFire.

I'm guessing this restriction involves checking if the Mobile Country Code is from the United States (310-316, I think). Since AT&T's MCC-MNC is 310-410, it's obvious the phone shouldn't be happy with it. However, with a SIM from GiffGaff (a virtual carrier on o2's network), I'm able to use AT&T in the US because their MCC-MNC is on the list, but not in the home position.

Armed with this information, I'm guessing I can take an AT&T SIM card, bump all the MCC-MNC's on the list down a position, and add a UK carrier in the 'home' position? That way my phone will look for the UK carrier and believe that it's a UK carrier's SIM, not find it and then move down the list to the roaming networks?

If anyone has any information on if this will work, or can point me in the right directions for the tools to try this, please let me know!

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migrated from superuser.com Feb 21 '12 at 16:59

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Maybe a silly question, but why not ask Vz to unlock it for ATT? In the UK carriers are obliged to provide this kind of service and I would imagine there is a similar setup in the states - even if it's not free it will be easier. Also, if there is a UK network in your home 'slot' then you'll be charged UK roaming rates irrespective of who provided the actual SIM card - and as the card won't have been registered by a UK network, it most probably won't work at all. –  George Pearce Mar 2 '12 at 11:54
    
you may want to ask also at howardforums.com, it is a well-established community about cellphones –  lupincho Apr 5 '12 at 21:27

4 Answers 4

Afaik Verizon can only unlock the phone completely and not block certain carriers.

Until the iPhone 5, there was no model that supports CDMA and GSM.

The reason your phone doesn't work on an AT&T network (or most international networks for that matter) is because AT&T doesn't run a CDMA network.

http://support.apple.com/kb/ht3939

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I don't think that you would (and should) be able to do that. AFAIK the SIM cards store data on an EPROM, which means you cannot rewrite it. Furthermore, this data is most often encrypted.

What you could (theoretically) do is:

  1. Get a SIM card reader and download SIM data from your AT&T SIM card.
  2. Decrypt SIM data.
  3. Alter SIM data and fix CRCs.
  4. Encrypt new SIM data.
  5. Write new data to an empty SIM card.

I have strong doubts about how legal steps 2 and 4 are and even stronger doubts you can complete these and step 4 successfully with publicly available information.

That said, searching for rewrite sim card and having a look at this Hack-A-Day project might help you on this quest.

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1  
Do you mean PROM? EPROM stands for Erasable Programable Read-Only Memory –  Fake Name May 7 '12 at 9:58

I once tried to change the MCC and MNC codes to my country, my iPhone is AT & T and tried changing the codes to the network (Claro) in Dominican Republic available since I jailbreak my iPhone with iOS 7.0.4 but only it worse, so I rebooted and immediately submitted to the welcome screen, and when trying to activate the SIM card aT & T did not work, did not work with the contract that I have in my country, so I restored

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I don't think Verizon is to blame for this. This is a technical issue. The Verizon iPhone 4 uses Qualcomm MDM6600 chip capable of doing CDMA and GSM; however, Apple failed to provide support for GSM, so from the hardware point of view alone it is useless for GSM.

Verizon iPhones only work in select European countries. See the list here.

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4  
The submitter is asking about the iPhone 4s. What you say only applies to the iPhone 4 –  jackslash Feb 28 '12 at 22:18

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