Sorry - I should have been specific in my previous posts... when I flashed, I performed the full procedure (eMMC and rootfs). I'm hoping it doesn't come to that... I'll see after I talk with T-Mobile again tomorrow. I re-read through some of the transcript... it's too bizarre for words. I'm pretty sure it's the SIM, as the "Enter code to remove operator lock" (which the TM rep insisted meant the phone was carrier-locked) only appears when the SIM is installed.