I recently had to factory reset my MetroPCS ZTE phone. Now when I put the SIM card in from my Huawei it won't connect to the carrier data network, it only works on WiFi.
Try going into
Settings -> Wireless & Networks -> Mobile Networks -> APNs and make sure the MetroPCS APN is selected.
Here is what mine looks like (I am on t-mobile, which is why I have that selected). Your list may be different.
If this doesn't work, give MetroPCS a call and have them re-add the device to the network on their end.
MetroPCS has some kind of marriage between the SIM card and the device. I have been trying to work around this. Else, pay MetroPCS 15$ a pop to change phones.
I have 3 phones I'm working with, 2 unlocked 1 MetroPCS locked. The only SIM card that will work is issued and activated by MetroPCS. Even the unlocked cell, I had to take it in to store and they remarried the SIM. So you can't just swap in an emergency for any reason. Not even BYOD and it's unlocked!