For most mobile carriers around the world, building a 5G network is going to be crushingly expensive, but AT&T has a cost-efficient plan: Use a $6.5 billion U.S. contract to upgrade cell towers with hardware for a national emergency first responder network, then upgrade the software to add 5G support. AT&T hinted at the idea earlier this year, but FierceWireless notes that CEO Randall Stephenson used an investor’s conference today to confirm the company’s intentions.

“To build out this FirstNet capability, this first responder network, we have to go climb every cell tower. Literally, we have to go touch every cell tower over the next couple of years,” said Stephenson. “We’ll be equipping every single cell site for 5G such that when 5G is ready to go, when it’s ready for prime time, our turn-up of 5G is a software load, it’s a software upgrade.”

Stephenson’s comments suggest that AT&T could light up a large-scale, perhaps national 5G network at some point in 2019 with the flip of a switch. Thus far, the carrier has promised to launch initial mobile 5G services in 12 cities by the end of this year.

While the plan might sound like a trick to turn public dollars into a subsidy for AT&T’s 5G network, the reality is more complex. Consumers perceive mobile network upgrades as performance improvements on their devices — faster speeds, fewer dropped calls, and sometimes better battery life. But actually achieving those improvements requires carriers to place new hardware on their towers, a process that requires updated components, regulatory approvals, and ultimately people to…