MetroPCS uses TMobile towers. If the phone is paid for, have Verizon obtain the SIM unlock code for you. (They're required to by law. If they tell you that they can't or thy won't, just let the sales rep know to inform the store manager that you're filing a formal complaint with the FCC for non-complaince. Then do it. Go to
FCC Complaints and fill out the form. (Not even Verizon is big enough to ignore an FCC show cause order.)
They may give you a website to go to, to request the code, and it can take up to a week for them to gt it (they have to request it from Samsung).
You'll be able to get 4G data now, but if and when TMobile expands to 1900MHz, you won't when you're in those areas.
