“Writing a telegraph circuit was like writing a recipe for a field technician,” he said. “A lot of legacy systems are still around here. I’ll be long gone before they will.”

Some other older employees besides Kevin Stephenson think the 2020 target will come and go, but basics won’t change.

The 2020 effort “is just a start,” said Kenny Williams, 64, a testing technician and the head of Ms. Cunningham’s union local in Southern California. “I’ve inoculated my people against worrying. They need a fiber network for this that doesn’t exist out here yet. Seventy percent of my folks are safe; the other 30 have to be found jobs, or they’ll take the golden handshake” and retire.

As he sees it, much of the urgency comes from the threat of Google. In 2015 Google Fiber, Google’s high-speed Internet service, caused AT&T to do something uncommon in its history: lower its prices because of competition. “In 40 years here I hadn’t seen that,” Mr. Williams said. “Their people aren’t in unions — we’re a lot more on AT&T’s side than theirs.”

AT&T recently began rolling out fiber in about 50 cities in the United States, in what it hopes is a bigger move than Google can make. Still, putting a cloud system all the way across a diverse, continentwide network will take years, which is why Mr. Williams feels safe.

Face to Face With Google

What happens next at AT&T — and how fast that will happen — is a matter of disagreement in the Stephenson family.

“I go out to houses away from the cities, and there’s not a lot of fiber there,” Kevin said. Fiber would open the way for all that new technology. He takes comfort in looking at patches linemen did on fiber systems decades ago — from both the jury-rigged craftsmanship and the way they have endured.