AT&T yesterday unveiled free robocall blocking for postpaid smartphone customers.

Named Call Protect, the service blocks some fraud calls at the network level before they reach customers' phones. In other cases, when it's less clear whether the call is fraudulent, Call Protect doesn't block the call but shows "suspected spam warnings on the incoming call screen which let customers choose whether or not to answer calls that originate from a suspected spam source," AT&T's announcement said.

At least for now, the service is available only for AT&T postpaid wireless customers with iPhones or Android phones that support AT&T's HD Voice technology. Call Protect is not automatically enabled. Instead, customers can add the feature in their AT&T account settings or the Call Protect app for iPhone and Android. Some Android users complained in the Google Play store reviews that Call Protect doesn't support unlocked devices like the Google Pixel.

AT&T warns that the network-level fraud blocking "[m]ay inadvertently block wanted calls," but customers can adjust the settings "to turn off blocking or allow specifically designated numbers." Customers can view a list of blocked calls in the Call Protect app. While network-level call blocking works across the AT&T network, the suspected spam warnings displayed on the incoming call screen will only work in the AT&T HD Voice coverage area. HD Voice provides clearer sounding voice calls over LTE; you can check out the HD Voice coverage area at this link.

Call Protect also has a "Temporary Call Block" feature that lets customers block specific phone numbers for up to 30 days at a time.

AT&T has a somewhat odd recent history with robocall blocking. In May of this year, AT&T CEO Randall Stephenson said that his company doesn't have "permission" or "the appropriate authority" to block robocalls, even though the Federal Communications Commission had clearly stated that the carriers do have that authority.

FCC Chairman Tom Wheeler stepped up the pressure on robocall blocking in July, urging carriers to offer free robocall blocking services. In response, AT&T agreed to lead an industry "strike force" to accelerate development and adoption of robocall blocking.

“Nuisance calls are an industry-wide problem that unfortunately affect many people,” AT&T marketing executive Jeff Bradley said in yesterday's announcement. "We’ve listened to our customers and know they want a network that provides tools to proactively assist in blocking nuisance calls."

AT&T appears to be ahead of the other major US carriers in robocall blocking. Verizon offers the ability to block specific numbers but recommends using third-party anti-robocall tools for a more comprehensive solution. T-Mobile USA says it is currently unable to "selectively block incoming calls or texts from individual numbers through the network," but notes that certain phones offer that capability on the device itself. Sprint offers a service to block specific phone numbers.