Is your phone S-OFF? If so, this method should definitely work. S-ON, I am not sure. In my opinion the main issue is you are on stock firmware and it doesn't allow you to modify. Flash the modified firmware and SIM unlocking will be easier. For details on activating WCDMA and switching to gsm mode using network app etc, read my thread http://forum.xda-developers.com/spri...tries-t2847461
Now I'm on InsertCoin_M8_3.0.4 ROM but nothing worked. I attached screenshots. Notice build version.
Downloading ".54.654.15 Modified Firmware....removed boot, hboot & recovery (fastboot flashable)" as you recommended, will try that ROM. Hope that helps.
As for QPST configuration, do you think if I forcefully switch to from LTE/CDMA to WCDMA mode that might work?
Do you know how to manually switch RADIO ON?
Seriously I have no idea whats wrong with the phone...