Unhappy [Q] Help! My Atrix won't recognize any network

This is an unmodified AT&T Atrix4G, which is supposed to be unlocked, but it was a warranty replacement and I believe it was carrier locked by the first owner, before ATR&T gave it to me. Last year, AT&T's unlock code didn't unlock it, and they and Moto both claimed to be stumped when we found this out last year. The phone did recognize AT&T NVMO SIMs, but would only say "network error" when I tried a T-Mob SIM.

So this week I went back to T-Mob, thinking maybe the phone IS unlocked but needs a T-Mob APN entered to work with a T-Mob SIM. Phone was working fine, and the T-Mob guy tried to boot the phone with a T-Mob SIM card in it. The phone asked for an unlock code, we put in the one AT&T had previously generated (and confirmed, no error there) and instead the phone rejected the SIM and said "emergency mode only".

Now, it won't recognize any SIM card, not the original AT&T card (AT&T also supplied a new card in case the old one was the problem) nor the T-Mobile. All it wants to do is boot to emergency mode, or ask for an unlock code again.

I've tried the factory reset cold-boot, that didn't help either.

The phone has just gone psychotic and doesn't like ANY SIM card. Is that nuts or what?

Does anyone have any idea what I can do to get the phone working again? With AT&T or T-Mob, I don't care, I'd just like it to work as a phone again, even if that wipes all the data from it.

AT&T's store, and their local "tech center", were both dumbfounded. They claim they've never seen a phone that just won't work, won't unlock, won't take any SIM card before.
Damned Atrix!Damned Motorola!Damned AT&T!Damned Google!
"Matilda, she take me money and run Venezuela."