Verizon now offers a free version of its Call Filter service, which lets customers get alerts when a call is likely spam, report unsolicited numbers, and automatically block robocalls based on their preferred level of risk. The service was previously $3/month/line, although a premium version with additional features (such as advanced caller-ID and personal block list) is still available for the same price. Only post-paid wireless customers are eligible, and they must opt in to receive the service. Features vary slightly by device. T-Mobile already offers a similar service. Verizon also announced that it's making progress in implementing STIR/SHAKEN, a technology that securely authenticates caller-ID info to deter number spoofing. T-Mobile has already implemented STIR/SHAKEN and AT&T also recently announced progress in its implementation. STIR/SHAKEN is more effective the more telecom companies implement it. The FCC has publicly threatened to impose new regulations if the industry does not do more to address the issues of robocalling and number spoofing