I doubt MetroPCS will activate the phone on their network, but you should be able to use it on other GSM networks. To get data and MMS you'll have to change the APN settings, which I believe you can do without rooting the phone. You will not be able to get 4g LTE data though since just about all carriers use unique channels.

I have 4 Samsung Galaxy S4's from Verizon which I got about a month ago. I have had some issues with Verizon and am thinking about canceling my contract and going with another carrier. A VZW customer service rep said that I could keep the phones for free, but I am not so sure. If they are correct, can the Verizon S4 be set up to work with full functionality on other carriers such as T-Mobile or MetroPCS? (I mention those 2 since they offer a $100 family plan for 4 phones, but coverage and speed may not be as good as Verizon.)