Hi GT...I did exactly this--I took a 4.1.2 S3, backgraded it to 4.1.1 (using downloads from this site, Samsung, etc.) and it works like a charm....*but* when you enable the "secret codes menu" and input the unlock sequence, *#197328640# then do:
Main Menu
[1] UMTS
[1] Debug Screen
[8] Phone Control
[6] Network Lock
there is then supposed to be Options [3]Perso SHA256 OFF
but instead there is nothing!
I have done the same thing with an ATT S3, worked like a champ.
I live in Brazil, and the same SIM from the ATT doesn't do anything in the USC phone--no unlock code is requested, just nothing, no signal.
Any ideas? I love the phone and am seriously considering having it flashed to Cricket or something just to unlock it.
Sorry for the long post--options or do i sell it on ebay and get another ATT unit?
I own the phone but USC says I need to be a current subscriber. I am arguing with them that they have to unlock it for me, I was out of contract and moved to Brazil, cancelled my account and then *head slap* realized I needed to unlock the phone.
My daughter laughs at me because she has a verizon S4--worked like a champ the minute we got off the plane and got a SIM card.