[AT&T, Rogers, Bell, Telus Samsung Galaxy S III] MyronJ906:
I didn't want to post more in the thread in development since they seem to be looking for specific causes, issues, etc. But I figured we could discuss some extraneous variables that no one has mentioned yet here. You never know what could be important. We're trying to look at obvious causes and it's not necessarily something obvious. Some people are losing IMEI on their very first flash (flashing to get root for example) so there has to be something else, even if it's just a specific version of recovery.

I still have my IMEI in tact (so far), but this is my pretty much exact history. I am interested in knowing if anyone who has followed similar procedures has lost their IMEI yet.

I know there are many of us around here who have not (yet?) lost our IMEIs. There has to be something different from our procedure versus everyone else's. There are also many variables that could come in when people are flashing.

Me? I'm of the opinion that this is some freak variable that no one is giving any attention to. I could be wrong, but me being wrong isn't going to destroy the world. Because of that, I would like to share my own process here with excessive details hoping that it helps out.

I STILL HAVE MY IMEI. These are my variables, and my history.

preemptive tldr; After initial CWM flash, I've always downloaded at home over WIFI directly from the phone. At home, I get strong signal even when not connected. Non-LTE area. I have not transferred a ROM to my phone via MTP or flashed from external SD Card. I have not wiped caches. Only Wipe data/factory reset at the most. Latest AT&T CWM from Rom Manager. I have followed these rules and stipulations every time and still have IMEI in tact. As you can see, I have had several flashes. At least 3 AOKP builds, 2 or 3 CM10 builds, several miscellaneous zips, and even a soft brick in between

1. The day I got my Galaxy S III (7/13/2012), I rooted and flashed CWM using this method on Youtube http://www.youtube.com/watch?v=UrxZy7H8VqY&feature=player_embedded through my laptop with the USB cable that came with the phone

I did everything using my internal storage since I didn't have my SD card back yet (let my brother borrow it).

2.I rebooted back into stock TouchWiz and tried to use it for a while, decided it wasn't for me so I downloaded Rom Manager Premium (and Rom Manager). I updated my CWM to the latest AT&T available there. I DID NOT (and refuse to) use CWM touch. (CWM Touch lead to some issues on the Atrix with people deleting their PDS partitions without confirmation).

3. I used tapatalk on my phone to read the AOKP thread. Decided that I wanted it so I downloaded it right there through whatever browser I was using.

I rebooted into recovery, went to wipe data/factory reset. Confirmed it, then flashed AOKP + ICS GAPPS. No problem.

Whenever I updated AOKP, I would download at home over WIFI just as the first time. I just dirty flashed. No cache wipes, ended up with no ROM issues (except random reboots.

4.I decided to test and see if the random reboots were AOKP or my phone. I decided to flash Diet ICS. Once again, I downloaded it over WIFI at home (the ONLY way I download ROMs for this device since it's worked for me so far). Except this time, my battery died while flashing (NOOB MISTAKE!) SOFT BRICK. Phone wouldn't charge the battery either. I had to go buy a universal battery charger from Radioshack. Once I charged, I could get into download mode. Reflashed CWM (same tar) through a newer version of Odin (3.something) because I thought it was gone.

5.REFLASHED AOKP. Wipe data/factory reset. Confirm. IMEI still working. Any updates that might have come during this time, just reboot into recovery and dirty flash.

When the AOKP version that required a full wipe was released, I rebooted into recovery and once again, wipe data/factory reset. Confirmed and flashed the ROM + gapps. No issues (except my random reboots still...my SGS III didn't like AOKP)

6. Flashed CM10 + SuperSU + JB Gapps (Wipe data/factory reset. Flash CM10, Flash Gapps, Flash superSU). The 2(?) CM10 updates since then, I have flashed just by flashing over my existing CM10. Also flashed the camera-fixer zip the same way.

Restated tldr; After initial CWM flash, I've always downloaded at home over WIFI directly from the phone. At home, I get strong signal even when not connected. Non-LTE area. I have not transferred a ROM to my phone via MTP or flashed from external SD Card. I have not wiped caches. Only Wipe data/factory reset at the most. Latest AT&T CWM from Rom Manager. I have followed these rules and stipulations every time and still have IMEI in tact. As you can see, I have had several flashes. At least 3 AOKP builds, 2 or 3 CM10 builds, several miscellaneous zips, and even a soft brick in between