##3282# works but it requests a SPC code.
This is so weird. I tried again resetting the phone with the T-Mobile SIM card in (I live in a refarmed area) and I get no service at all. No bars, no voice, no data, even after setting up the APN.
Then I tried resetting it again with a Mexico Telcel SIM card. I set up the APN and it now says "T-Mobile-TELCEL" like it's roaming on T-Mobile (then why don't I get service with the T-Mobile SIM?) and guess what, I get perfect LTE service (roaming, of course) but no voice. I tried calling my Telcel number from a different phone and I get sent straight to Voice Mail. I also tried placing a phone call and I get a message that says that the phone is in Airplane Mode (it's not) and asks if I want to turn on the cellular connection. I click Turn On but nothing happens and phone calls still fail.
It seems to me that somehow the GSM bands are there, but Verizon crippled the device so it can't be used outside of their network. Maybe they can be enabled manually or in a future firmware update, I don't know.