"The problem is the bad guys aren't just sitting still. Instead of making up phone numbers, they're getting real phone numbers. And now their real phone numbers are authenticated, they look like they're good and they get through," says YouMail CEO Alex Quilici who believes technology like Stir-Shaken isn't enough to crack down on spam calls. Quilici says there also needs to be more enforcement. "You want enforcement to go not only after the bad guys, but some of the carriers that are supporting them," says Quilici.