First Responder Data Prioritization

How does the data prioritization work for first responders? Does it have to be activated when you need it? Will a go unlimited line be given priority?

I was a longtime Verizon customer. Kept the old grandfathered unlimited line until okay month. I went over to Firstnet and put my wife on AT&T. I definitely liked Verizon service better, but not for an extra $100 a month. Now that they are supposed to offer a discount I might come back.