Believed to be the first call-authentication partnership in the U.S., AT&T and Comcast have announced the imminent arrival of a new Caller ID authentication system that is aimed at fighting the growing number of robocalls.

This system is meant to let users of the two networks know when a genuine caller is on the other end and not a spammer. And it’s rolling out later this year.

The two carriers say they’ve completed cross-network tests of the new security protocols (SHAKEN/STIR) that use digital certificates to separate genuine callers from spammers. “An exchange of authenticated calls between two separate providers’ voice networks that is believed to be the nation’s first” has been completed, part of the announcement post notes.

The new protocols will prevent calls that show a faked caller ID from going through and in the process mark them as unverified. Although it’s a good step going forward, unfortunately, it won’t initially cover all AT&T and Comcast users. Apparently, the initial rollout will only identify legit calls and not spammed ones, meaning robocalls will still go through but show up as unverified.

Also, it’s worth noting that since this partnership involves only two carriers, the new Caller ID tech won’t be able to validate calls from other networks. But this should change once every other carrier installs the new protocols.

Related: The best AT&T Android phones