Traditionally cdma carrier phones are not compatible with gsm carrier devices. so verizon and sprint phones never worked with att and tmobile phones.
However... someone on WP central stated that most newer LTE Verizon phones were coming unlocked, and that the 8x on Verizon also had a SIM card tray. I went to the Microsoft store yesterday and the associate confirmed it and showed me the SIM card tray. So, I plan on trying out the new Verizon Nokia flagship with a mobile SIM card and see how it goes. Of course I'll probably have to configure things like mms settings but its worth giving it a shot if the new 928 will have a SIM card like the 8x does.