[T-Mobile, Samsung Galaxy SIII] ingenious247:
I ran a couple of searches on Google( and in this forum) to try and find the original thread about this issue, however I didn't find it so I'm posting here in case anyone else can be saved by this fix.

First, some background:

I have been running CM10 Nightlies for almost a month now, also using the leaked Jelly Bean radio version T999UVLI2 with absolutely no problems. Everything was working great, data, ROM, etc. (Prior to that I was on Stock ICS, rooted. Had not run any custom ROMs whatsoever).

I noticed after flashing the latest CM10 Nightly (Oct. 14) that my phone had started acting a little weird - nothing drastic mind you, just a few glitches here and there. The weird thing was, all of the previous nightlies I had flashed pretty much worked flawlessly for me, minus a volume issue when in-call which was a known bug. I had done a clean flash as I always do, so I attributed the glitches to a possible bug or two in the latest Nightly and figured it would probably be resolved in the next release. No big deal.

Yesterday afternoon, after reading a thread that is tracking all available T-Mobile radios by region (to see what works best in your area) I saw someone who posted that the T999UVLI3 radio gave them the best speeds, and they happened to live in the same exact city as I do here in Southern California. So I decided to flash the new radio using Team Sonic's Modem flasher, which I used in the past to flash the LI2 radio that I was currently on. I flashed the T999UVLI3 radio and found that it did indeed provide better data speeds than the LI2 radio, so I was pretty happy about that. Used my phone all day/all night with no problems, everything was great.

I always leave my phone plugged in at night so that I have a fresh charge in the morning - this morning I turned off my phone while it was still plugged in as I leave it off during the drive to work to save a little battery before I start my day. Typically I unplug it first and then turn it off, but not always. So nothing really out of the ordinary there.

I get to work and turn on my phone, and all of the sudden I notice that I have no bars - at all. It doesn't say "T-Mobile" at the bottom of my lock screen. I figured it was just taking it's time booting up, which would be very weird as it never does that, but I waited. And waited. Nothing. Now I'm starting to get a little worried.

Went into settings and checked "About Phone" and it said my Baseband version was "unknown". Oh crap. IMEI, unknown. Serial number, unknown. GREAAAAT

For the life of my I couldn't imagine how this could happen when I didn't even do anything from last night to this morning. I started going over everything I had done recently to my phone.. the power off while plugged in, the nightly update to the Oct 14 build, then it hit me.. the new radio version. Maybe that was it

In a desperate attempt I booted into recovery and ran Team Sonic's Modem Flasher and flashed back to T999UVLI2. Rebooted the phone and... BAM! Back to normal. W...T...F..?

If anyone loses their IMEI, before going through the entire injection fix process, try reflashing a radio. Worked for me!

Any theories on why this happened? Many people have been using the T999UVLI3 radio, I believe without any issues.. but I could be wrong. Anyone flashed that radio and lost their IMEI?