AT&T and T-Mobile fight Caller ID spoofing with number verification system

A smartphone with an incoming phone call from an unknown caller

EnlargeGetty Images | Tero Vesalainen

In fact, USA mobile carriers T-Mobile and AT&T revealed on Wednesday that they are teaming up to bring call cross-network call authentication protections to their subscribers.

The target is caller ID spoofing, a technique used by spam callers and robocall systems to try to persuade you to answer the phone.

The FCC, which has named stopping illegal robocalls as its top consumer priority, said last month that carriers have been slow to roll out options for curbing unwanted spam calls. For example, AT&T told Ars that it's using Caller ID authentication as one data point in its anti-robocall algorithm but that it isn't blocking calls exclusively based on whether they aren't authenticated.

An agreement on SHAKEN/STIR was inked between T-Mobile and Comcast Xfinity Home land lines in April 2019, as well as between AT&T and Xfinity Home land lines, and now AT&T and T-Mobile are joining up the triangle.

The carriers jointly announced SHAKEN/STIR (or STIR/SHAKEN) deployment this morning. Verizon is also likely to implement the technology on its network in the coming months.

In brief: This technology lets the end-user know that an incoming call is really coming from the number shown on the caller ID display. Most calls today aren't subjected to the SHAKEN/STIR test, T-Mobile said. For the time being Caller Verification only works on 12 smartphones from Samsung and LG, but the carriers promise to make it available for other models as soon as possible. Most legitimate calls today are not verified through SHAKEN/STIR, so a call's unverified status isn't enough on its own to trigger a block, AT&T said.

As we've noted in previous articles about the robocall nightmare, SHAKEN/STIR (which stands for Signature-based Handling of Asserted Information Using toKENs and the Secure Telephone Identity Revisited) is the standard that the FCC recommends carriers use to digitally verify phone calls. Customers of Metro by T-Mobile will also be included in the new cross-carrier service.

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