Verizon yesterday said it will make spam and robocall blocking features free for all wireless customers starting in March, about two years after AT&T and T-Mobile began offering free robocall blocking.

"In March, we will be rolling out our free spam alerting and call blocking tools to all of our wireless customers whose smartphones support these features, including iPhone and Android devices," Verizon's announcement said. "There will be more information on how to sign up for the free service as we get closer to launch."

Verizon added call and spam screening features more than a year ago to its $2.99-per-month Call Filter product, which also lets customers see contact details for unknown callers. Verizon pointed to research showing that its system "correctly identified potential problem phone numbers approximately 93.6 percent of the time."

"This service identifies spam callers and unknown numbers by name and shows an innovative risk meter that displays the level of spam risk associated with a call," Verizon said. "If a call meets Verizon's spam criteria, the incoming call screen will display a spam label."

Verizon said it is "continuously updating our algorithm" and has "identified nearly 300 million numbers associated with spam and robocalling."

The free service will be deployed in an app, a Verizon spokesperson told Ars. Users will be able to choose their desired level of filtering, since "some people have legitimate reasons for [receiving] robocalls like prescription notifications, school closures, etc.," Verizon said.

AT&T began offering free robocall blocking in December 2016, and T-Mobile announced free robocall blocking in March 2017. AT&T's free version includes spam-call warnings and automatic blocking of robocalls that attempt to defraud consumers, but AT&T charges $3.99 a month extra to automatically send suspected spam calls to voicemail. (Then-FCC Chairman Tom Wheeler had urged carriers to make call blocking free to consumers in July 2016.)

Sprint's service costs $2.99 a month, and consumers can also buy third-party tools such as Nomorobo and RoboKiller.

T-Mobile launches another robocall service

T-Mobile last week launched another free blocking service named "Caller Verified," though it's initially only available for the Samsung Galaxy Note9. "Caller Verified will be available on more smartphones later this year," T-Mobile said.

T-Mobile said the Caller Verified service is the first in the industry to use the new STIR/SHAKEN standards.

"STIR and SHAKEN use digital certificates, based on common public key cryptography techniques, to ensure the calling number of a telephone call is secure," telecom software provider TransNexus explains. "In simple terms, each telephone service provider obtains their digital certificate from a certificate authority who is trusted by other telephone service providers. The certificate technology enables the called party to verify that the calling number is accurate and has not been spoofed."

STIR/SHAKEN will work best when it's adopted by all phone providers. Besides T-Mobile, phone providers including Verizon, AT&T, Comcast, and Cox have committed to implementing STIR/SHAKEN. FCC Chairman Ajit Pai has been urging the industry to speed up deployment of the new frameworks.

The free Verizon service coming in March won't include STIR/SHAKEN at launch.

"STIR/SHAKEN is something being added on the network side of things, and we anticipate it to be up and running this year," the Verizon spokesperson told Ars.