TMO acquired MetroPCS partly because the latter uses the same band for LTE that TMO does. But I don't know if the N4 will work on MetroPCS. I'm sure someone has tried.
MetroPCS still has a lot of CDMA, but it's also had LTE in markets such as Las Vegas since September 2010. It also was (still is?) the first U.S. operator to offer voice over LTE (VoLTE).