Twelve cell carriers, including the four largest — AT&T, Sprint, T-Mobile and Verizon — have promised to make efforts to prevent spoofed and automated robocalls.

Announced Thursday, the pledge comes after 51 U.S. attorneys general brokered a deal that would see the telecom giants roll out anti-robocalling technologies, including a way of cryptographically signing callers to wipe out phone number spoofing. Known as STIR/SHAKEN, the system relies on every customer phone number having a unique digital signature which, when checked against the cell networks, validates that a caller is real. The carrier near-instantly invisibly approves the call and patches it through to the recipient.

Robocalls are illegal, but are a billion-dollar industry. Many of these automated, robot-dialed calls imitate a cell number area code to convince unsuspecting victims into picking up the phone. Often robocalls try to sell products they don’t need — or worse, try to con victims out of cash.

The hope is that STIR/SHAKEN would weed out most robocalls. The system would verify real callers while the billions of illegal or spoofed robocalls made every year would fail.

So far to date, AT&T and Comcast have tested the new anti-robocalling system, and AT&T and T-Mobile have also teamed up to use the technology to fight robocalls. But the system works best when every carrier uses the technology, allowing calls to be checked even as they traverse between networks. By getting Verizon (which owns TechCrunch), Sprint and the other cell giants on board, the attorneys general hope the cooperation will vastly reduce the number of robocalls each year.

CenturyLink, Charter and U.S. Cellular have also signed up to the pledge.

There’s a catch: No deadline was set, allowing the carriers to take as long as necessary to roll out the technology. That may not be good news for those seeking immediate relief. Although all of the major networks have already made some progress in testing the new anti-robocalling system, few have said exactly when their service will be ready to roll out to consumers across the country.

The Washington Post first reported the news ahead of Thursday’s announcement.

The pledge comes just weeks after the Federal Trade Commission and the Justice Department took coordinated action against close to a hundred individuals and companies accused of making more than a billion illegal robocalls.