[Galaxy S III Q&A, Help & Troubleshooting] Jarmezrocks:
Notes from what I discovered reviving this phone several times yesterday.

1). The EFS folder once upgraded to Android 4.3 cannot return to an earlier version of Android** there is an exception to this and I will elaborate why

2). The EFS folder CAN be downgraded but only to about a version or so - I could get the IMEI to appear when I rolled back to 4.2.1, the phone was displaying signal but was not connected to the network for some unknown reason?

3). I suspect that the EFS Android version and firmware Android version need to be fairly close together? The modem.bin has something to do with the EFS version. ** I brought the Android version back up to the same 4.3 alone with the modem.bit however I was still not able to obtain signal.

4). Rolling back the Android version to try unlock the device from it's network proved to be fruitless - A possible subclause here would be that you may be able to unlock the device if you were planning to be on the same network but would kind of defeat the purpose wouldn't it?

5). After watching several clips on YouTube I am of the belief that the IMEI number for a device when it is sent for repair; is regenerated from scratch using the number under the battery and tools like a Z3X box. Note: These types of tools CAN and ARE being use for illegal behavior >>>PROOF, which only emphasizes what I am about to say...I STRONGLY suggest that you do NOT take your device to any local random person that claims they can repair your IMEI unless you trust them as they can quiet easily duplicate your IMEI number. I would recommend a reputable repair business or a Samsung technical service.

6). The patches like in this thread only attempt to try keep the IMEI at a lower version whilst allowing modems from a new version to connect. They do not deal with incompatability of Android firmware version and the modem it's self, hense why this patch doesn't work for everyone. In my case it didn't and I had A) Return the EFS to the stock version prior to corrupting (leaving anything patched would equal no signal) B) Flash the phone back to the same firmware; in my case was Telstra branded firmware version 4.3.

7). Flashing back to the Android version you were running before corrupting your IMEI/EFS then you are likely to get it back only if you run the same modem file.

8). Future reference - when considering flashing new firmwares I would suggest backing up your EFS as you do a nandroid backup further to this I believe that if you ever want to return to your standard carrier branded firmware that in order to do so would require you to flash firmware that is NEWER (a whole Android version) than the version that updated your EFS and using an unpatched EFS when you do OR you will always require patching forever.

See my post I responded to you in the other thread.

As a suggestion I would try these things. Backing up your EFS anyway using EFS Pro. Opening a

copy of

your efs.img with Linux Reader and exporting the recovered files.

I would then try flashing revolutionary again and if you have signal and can make calls again but you want to be back on firmware that allows use of a local modem then make a backup again of the EFS using EFS pro. Export again using Linux Reader and then use a tool like Folder Match or Min Merge to diff the files and make note of what you discover.

If you are happy with just being able to make calls again and you don't wish to partake in a voyage of discovery and information then stop reading NOW

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Disclaimer - I take no responsibility for your phone becoming bricked

Try flashing a new modem on the revolutionary that matches the either your region/service provider (note the firmware version of the modem for your region will have to be the same or greater than revolutionary for your EFS to work again) or the stock Android you wish to return to (this will likely need to be 4.3 or greater you CANNOT return to 4.1.1 by any means that I know of so give up that idea). If you keep signal after doing this then backup the EFS directory once more. What I am about to suggest from here will require you to backup your internal SDcard.

Get the standard firmware (again has to be at least 4.3 - your EFS has been upgraded and cannot accept an older version) and repackage it using tools that you can find on the forums such as TAR.MD5_PACKAGER (search and you will find it)

Unpackage the firmware, place your choice of modem.bin files (again has to be at least 4.3 to work with updated EFS) in the firmware, repackage it. Using Odin and choose PDA and select your modded firmware.

If you note that you have lost signal yet again (by signal I mean you cannot make calls but you have bars of reception) then I would say that you are stuck using the modem file that has come with revolutionary (the one that upgraded your EFS) and you can try flashing the modem.bin from revolutionary and see if that allows you to make calls again using stock firmware. If not then I would try restoring your last backed up EFS. When I say restore your EFS I mean the extracted contents of your backup efs.img using Linux Reader DO NOT restore efs.img using EFS Pro it will only re-apply the corrupted file structure of your efs.img; You will have to manually delete the contents of the efs folder in the root of your phone but not delete the efs folder its self (it contains special permissions). Copy the extracted data you got from your corrupted EFS folder from your SDcard and paste it inside the efs folder in the root of your device. Reboot the device into recovery. Choose fix permissions. Reboot and see what happens then? You may find you get signal and calls can connect?

If after all of this you still don't have reception, then I would say you are stuck using revolutionary and would suggest you restore the first EFS the same way described above, flash revolutionary and just be happy with a working phone.

Note: I would have done exactly this yesterday had the phone been my own and I didn't have only a few hours to return it back to its owner in perfect working order.