The mobile application works by applying network-level monitoring and blocking of known spam calls using the company’s voice-over-LTE (VoLTE) network data capabilities. Since the network is IP-based, it resembles a traditional email spam filter by analyzing incoming calls and labeling them as spam. Second, the app will display an on-screen message warning users before answering their phones.

The app also features a temporary call block to manually block unwanted calls for up to 30 days. When spam calls are added to a filter list, users can select callers to block and have the numbers renewed after the filters expire.

AT&T’s VoLTE network was introduced May 2014 beginning with four states in the Midwest and is now available in 96 percent of its LTE coverage area. As such, there may be a small percentage of customers who will not be able to regularly use the Call Protect service.

In addition, a user’s smartphone also need to be compatible with HD Voice in order to use Call Protect, and should include most mid-range and higher-end devices produced during or after 2012, when mainstream LTE coverage began rolling out across the US.

The app is available free to download for AT&T customers on iOS and Android.