How Permanent is the Iphone 4S Carrier SIM unlock

[saqer]

I'm with Sprint and used upgrade on one of my lines to to get an iphone. I will give it to my brother to use while abroad. I will activate another phone on his line so we can still make use of the line while he's away, and the iphone 4S will not be linked to any Sprint line.

My account met the criteria for the unlock and I have already gotten the "Congratulations your phone is unlocked message through itunes." I have purchased a Rogers test SIM and though it is not provisioned it appears to be recognized by the iphone when I go to into Settings-About-Carrier-Rogers. My brother will be using a sim card from a carrier of the country he's traveling to. If my brother has to factory reset or update firmware on the iphone at any point while abroad and get it reactivated through itunes or wifi do you think it would reverse the unlock?

 

[QuarterSwede]

No. A carrier unlock is permanent.

 

[TriJetHero]

Carrier unlock is pemanent.

Restoring firmware doesn't effect it.

 

[saqer]

Thanks. I know the iphone 4S meant for US CDMA carriers have a block on domestic GSM bands. How can i tell if the carrier he will use abroad work with the sprint iphone? I looked something up called MCC-MNC and it looks like the CDMA iphones are blocked from using any domestic carrier. Could that also apply to international carriers? He will probably be using Vodafone.

The reason I ask this question because when I have traveled abroad in the past with my Sprint Blackberry that has GSM capabilities I once noticed that a certain international carrier's SIM will not work with it correctly.

 

[TriJetHero]

No it wouldn't

Only few operators use CDMA, most use GSM.
If it's unlocked it will take any GSM.

 

[saqer]

I am also curious as to learn any technical explanation for a single, uniform device like the iphone 4S that is identical hardware everywhere u go, but where the factory unlocked version would not work CDMA and the carrier unlocked GSM versions would never work on CDMA carriers and the CDMA released versions would never work domestically on GSM networks. Does that have to do with slightly different software or hardware versions?

I reckon the reason they are designed like this so that roaming agreements are not breached, but what exactly within the phone prevents a factory unlocked version from being activated on Sprint or Verizon? I have seen reconditioned iphone 4 and 4S devices before that were on Carrier A and were reidentified on carrier B? Does that have to do with the way the Serial Numbers are loaded into carrier databases?
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No it wouldn't

Only few operators use CDMA, most use GSM.
If it's unlocked it will take any GSM.

Just not domestic carriers, right?