can i use an unlocked iphone 5s on metro pcs?

I recently got a new phone on my Verizon plan. I gave my unlocked iPhone 5s to my boyfriend to use on his Metro PCS plan. We went into the store and he got a new SIM card for the phone; it was making/receiving calls and texts and seemed fine. One problem, he cannot get on the internet unless connected to wifi. Does anyone know why this is happening?? Metro said it was a Verizon thing. Verizon said it was an apple thing, but we've tried going to and/or calling these places and even returning to Metro a second time. No one seems to know why this is happening. Anyone have any tips or has experienced this before??