Any unlocked GSM phone can be used as a MetroPCS upgrade phone. To make the upgrade, swap in a MetroPCS SIM card, and activate the phone online or in a MetroPCS store. MetroPCS is a prepaid carrier and does not offer discounted phone upgrades, as of 2015.
MetroPCS sells phones online and in its physical stores at full price, regardless of whether they are new activations or upgrades. Phones purchased directly from MetroPCS are guaranteed to be fully compatible with its network.
CDMA phones from carriers such as Verizon and Sprint are not compatible with the MetroPCS network. Phones from AT&T and T-Mobile are compatible if they are unlocked for use on any GSM carrier.