[AT&T, Rogers, Bell, Telus Samsung Galaxy S III] proxykid:
Hi,

After several days trying to unlock my phone and getting it bricked I finally managed to have it in a working condition and unlocked! I'm not sure if what I did unlocked it, but at least it's rooted and in working conditions.

So I decided to share my story and all the steps that I took to fix it. I would have written just the steps but somebody might find specific parts of the story useful.

Original Equipment and Status:

Phone: Samsung Galaxy S3 SGH-I747M (LTE version)

Carrier: Telcel

Country: Mexico

Original Stock OS: 4.1.1

Last working OS: Cyanogenmod 11 Nightly 20141221

Backstory

I'm having a roadtrip that will take a couple of weeks and I got a TMobile SIM to use during my trip through USA and Canada, however my phone was locked to Telcel.

CM brought me some couple of issues with the modem and network selection and as I live right next to the border and cross it every week or so, I was having a hard time switching between carriers and international roaming so I have to upgrade the modem to the latest one (From I747MUMBLL1 to I747MUMUEND3) and for some time I was able to select network operators but still it was locked.

No USSD / Unlock Code Fail

I found on the web there is a way to unlock SG3 for free through the hidden menu, but it didn't work for me but found out USSD codes no longer work in 4.3 so I restored the stock ROM for 4.1.1 (I have no idea how I managed to do this, but got it downgraded) I was able to get to the hidden menu and followed this instructions but I kept using multiple modem versions that aren't for JB the hidden menu didn't gave the option to generate the nv_date file. I think this was due the use of newer modem versions that didn't have the option to initialize the file.

Next attempt was to purchase SIM unlock codes without success, the providers I attempted were TheUnlockingCompany and CellUnlocker, neither of them were able to get me a code to unlock the phone

Also attempted to modify the NV_DATA file but well, it didn't exist in the /efs folder, there were other files but nothing related nv_data.bin. So I really needed to have that file to unlock it but no success in initializing it.

Third-party local unlock dealer

As all the attempts previously failed I needed to have my phone unlocked and was running out of time. So I took it to a local dealer who has more experience unlocking phones. This part I don't have all the info in whatever he did, all I know is that he was unable to work with CM and attempted to unlock it with a brasilian stock firmware, which got it bricked and it was getting more difficult to unlock it.

AFAIK I did have the old bootloader, but his attempts included upgrading the bootloader which includes KNOX and any attempt to restore old rom versions gave me the error

SW REV CHECK FAIL : Fused 1 > Binary 0

therefore it was impossible now to get back to stock 4.1.1 and attempt the older modem versions which at this stage found out could have solved the original unlock issue but .... too late.

His attempt with the brasilian stock ROM got the phone bricked and now instead of trying to unlock it I was trying to revive the phone, all my attempts in bypassing KNOX and downgrading the bootloader failed - also attempted to get back to 4.2 and 4.3 through CM 10.1, 10.2 and stock 4.1.1 but bootloader was too recent which prevented me to use those CM versions.

I was able to get it unbricked using CF-AUTO-ROOT - this is a life saver at least to be able to boot the phone, everytime I get a bricked status just by flashing this allowed to boot.

Phone kinda working: NO IMEI NOR ESN

Finally I decided to restore but directly to 4.3 stock for my original provider Telcel. The phone works now... kinda. It boots and gets signal, but NO DATA. I just found out IMEI/ESN information got lost and I didn't have any backup, yes I know I should have but whatever I was doing at least was not touching that information, but this other guy got it messed up.

One interesting thing is that even though there was no IMEI information, but original SIM card works to send/receive calls and SMS. Data doesn't work, but at least calls and SMS does.

Phone included KNOX and was preventing me to use the previously mentioned tool CF-AUTO-ROOT and found this tutorial: http://forums.androidcentral.com/samsung-safe-knox/352922-sprint-galaxy-s3-possible-knox-fix-cf-autoroot.html - this actually works but didn't give me the option to remove KNOX.

THe problem now is that any attempt to use SuperSU through USB debugging was blocked by KNOX but apps opened directly from the phone weren't, with this I installed CWR right away and TitaniumBackup, this last one allowed me to uninstall any KNOX crap. Rebooted the phone and no more issues whatsover in root usage.

As I only have 1 remaining day to have this phone in working conditions and it's christmas today I went on in trying to rebuild my IMEI.

Rebuild IMEI WITHOUT BACKUP

After lot of research and no friends which the same phone that could give their nv_data files, I found out THIS guide (again USSD codes not working so I used EFS Pro to switch USB modes) and basically this is what I did:

Download EFS Professional - Epic tool to work IMEI/ESN info and switch USB mode between MTP+ADB and DEV+MODEM+ADB

Download QPST version 2.7 build 323 NOTE: USE THIS VERSION, NEWER VERSIONS DO NOT INCLUDE RF NV Item Manager

Follow the instructions in the previously mentioned guide, but the USB you can switch it from EFS Pro under

Samsung Tools

.

It is really important to notice the IMEI number needs to be entered with the HEX checkbox enabled and in reverse.

You probably could do this straight from EFS Professional -> Qualcomm Tools, but this worked for me.

At the end of the guide there was no confirmation or any message the NV information was written successfully, so I just rebooted my phone and success! IMEI is back!

Just to test I tested my T-Mobile SIM and it works! - I'm not sure if this unlocked the phone or whatever the other guy did, but well the phone now accepts any SIM.

No Data / Stuck on EDGE

Now that the phone has the IMEI number and is unlocked I found out DATA still was not working.

I used the tools ESN, MEID and EUIMID Calculator to generate the rest of the missing information which was ESN and MEID. I entered this information in EFS Pro -> Qualcomm NV Tools, checked the boxes and clicked on write making sure the select box next to it was set to Phone.

Rebooted my phone and yes the information was there, however STILL NO DATA.

I came across this life savior - Load this file with NV Item Reader/Writer Some people on the thread say even their already working LTE data achieved better speeds with this.

Rebooted my phone and wallah! DATA and LTE are back! AND UNLOCKED!

What did I learn from all of this? DAMN KNOX and ALWAYS ALWAYS backup /EFS or whatever IMEI/ESN/MEID info is, even if you plan to use custom roms or not, or unlock the phone.

Link to useful tools and sites

CF-AUTO-ROOT - Fix a failed ROM update attempt in ODIN and/or apply permanent root.

ESN, MEID and EUIMID Calculator - Calculate the MEID and ESN based on IMEI

QPST version 2.7 build 323 - Qualcomm Product Support Tool - Modem and service editor

NV Item Reader/Writer - NV Information backup/restore

this life savior - Restore DATA LTE

SamFirmware - Stock roms