All information on the web points out that it WILL BE a global, GSM-ready phone. It is said to have GSM-capable radio. You can't do "global roaming software-only", since it wouldn't have a physical way to connect to any provider that would do the roaming.
For now, it gives me "The SIM card is from an unknown source" and "no SIM" and "no service", having a GSM microSIM card (hey, @ScottyDsntKnow, you are therefore wrong to think that GSMs cannot be microSIM).
Doing *#*#4636#*#* does not work on Droid4 for me, the code just disappears right after the last asterisk and nothing happens.
I have a XT912 with the same problem. I'm tired of the $80 smartphone plan and wanna switch to my old good T-mobile prepaid, but failed. Did you get this problem sorted out? If you did, I'll really appeciate it if you can tell me how.