According to new data from calling services vendor YouMail, AT&T’s customers received an average of 15.1 robocalls during the month of March, putting the carrier in the rather unenviable position of being the leading provider of robocalls among the nation’s largest wireless carriers.

YouMail’s data for March showed that T-Mobile placed a close second, with an average of 14.8 calls per customer in March, while Sprint counted 12.4 and Verizon counted 11.8. The firm said that Sprint saw the most growth in the volume of robocalls, with a 21% change over the firm’s February numbers.

Carrier March Robocalls/User Change from February AT&T Wireless 15.1 +14% T-Mobile 14.8 +10% Sprint 12.4 +21% Verizon 11.8 +13% Blue Wireless 3.6 +20%

The numbers arrive just before the FCC and FTC’s Stop Illegal Robocalls Expo on April 23, which YouMail CEO Alex Quilici will attend to discuss how carriers can better protect consumers.

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YouMail said it obtained its data from its “sizable” base of users, though the company didn’t provide specifics. The company’s CEO, Alex Quilici, said YouMail’s platform is able to monitor “hundreds and hundreds of millions of calls,” and that it can detect whether a call was a robocall by using a mix of audio-fingerprinting (seeing when the same or similar content gets picked up as voicemails), call patterns and behavior (unassigned numbers making calls or a high volume of hang-up numbers) and user complaints and comments on given numbers.

YouMail, which offers a visual voicemail service for iPhones and Android devices, also operates a Robocall Index that compiles the scope and location of the worst robocalling hotspots across the country by area code (Atlanta leads the list). The company said it has stopped over 1 billion robocalls from being made.

"While we can’t comment on the study because it’s not clear if their results are reliable or how many users per each provider actually engage with their service, we can tell you that we are committed to cracking down on and offering tools to block nuisance robocalls," an AT&T spokesperson said in response to YouMail's findings. "AT&T was the first provider in the U.S. to launch such a core network-based call blocking program. To date, AT&T has blocked more than 3.5 billion suspected illegal robocalls on its network, and that is in addition to the more than 128 million fraud calls blocked through AT&T Call Protect, a free service that automatically blocks fraud calls and provides screen alerts for suspected spam calls."

More broadly, the FCC has recently been looking into the issue to see how it might reduce the number of robocalls to consumers. The expo next week is part of that effort.

Article updated with comment from AT&T.