T-Mobile was the first to install the new standard — known by the acronym Stir/Shaken, a tortured reference to James Bond and martini preparation — in January, although it’s currently compatible only with certain devices. AT&T and Comcast have worked together to verify calls across their networks, and Verizon said it expected to finish rolling out the standard within the next few months.

For the new approach to be most effective, the vast majority of the industry, from cable landlines to mobile providers, must use the new protocol. That way, both ends of a call — a Verizon customer calling, say, a Comcast customer — can be verified.

Gaps would still exist, however. Most older landlines, the kind found more often in rural areas, cannot adopt the new protocol. And international calls cannot yet be fully traced, so scams originating overseas using a spoofed domestic number could slip through . But experts said the new standard would still make it easier to more quickly identify schemes coming from overseas — and other calls that couldn’t be fully authenticated — if the industry’s biggest companies adopted it.

“We believe that we will begin to see value once a critical mass of deployment has taken place, a bit like vaccinations, and the top dozen or so carriers should get us to that point,” Mr. McEachern said.

While the Federal Communications Commission has said robocalls are a top priority, critics have long complained that the industry and its regulators have been slow to address the problem. The industry has been working on the new protocol since at least 2013, and the F.C.C. has been criticized for not requiring a firmer deadline for its adoption.

A Senate bill that would establish a deadline has gained bipartisan traction. The Traced Act, introduced by Senators John Thune, Republican of South Dakota, and Edward J. Markey, Democrat of Massachusetts, passed a committee vote this month. Along with stiffening penalties and giving the F.C.C . more time to punish perpetrators, the bill would require all voice service providers — including those over the internet , such as Skype and Google Voice — to adopt call authentication technology within 18 months of the bill’s enactment.

“The phone companies say they are working toward this, but we really think it’s important to be required to implement this by a certain deadline,” said Maureen Mahoney, a policy analyst at Consumer Reports .