PhotoA test of caller ID services provided by AT&T, Verizon, Sprint, and T-Mobile found AT&T did the best job of telling which incoming call was legitimate and which was spam.

The study by HarrisX, a market researcher focused on the telecommunications industry, specifically tested how each carrier identified spam and non-spam calls. The tests involved both Android and iOS phones.

The study may carry added significance as consumers receive more and more spam and scam-related robocalls. Spammers often “spoof” the number from which they are calling, making it appear like the call is originating locally.

Increasingly, consumers besieged by robocalls are choosing not to answer calls from unfamiliar numbers. But the study authors say that can present another set of problems because important calls -- such as a job offer -- could go unanswered.

Test results

The tests found that AT&T’s Call Protect caught the most spam calls. That screener flagged spam calls 58 percent of the time.

Verizon was second with a success rate of 54 percent. T-Mobile identified 35 percent of spam calls while Sprint had a 1 percent success rate in the test.

While identifying unwanted calls is important, so is not flagging legitimate calls as spam. Here, AT&T was the winner, mistakenly identifying legitimate calls as spam only 6 percent of the time.

T-Mobile’s screener made that mistake only 15 percent of the time and Verizon was nearly the same, at 16%. The authors did not deem Sprint’s mistake rate relevant to the study since it only identified 1 percent of spam calls.

Overall scores

The study authors gave AT&T an overall score of 80 percent; Verizon earned a 72 percent rating, T-Mobile came in at 70 percent, and Sprint brought up the rear at 69 percent.

“When it comes to protecting consumers, the ability to differentiate between actual spam and legitimate calls is a crucial element of quality in the fight against unwanted calls,” the authors concluded. “By each measure of this study, AT&T significantly outperformed its competitors in identifying spam correctly.”

In addition to the carriers’ caller ID tools, there are a number of apps that consumers can use to block unwanted phone calls, particularly robocalls. They include Hiya, YouMail, NoMoRobo, and TrueCaller, among others.

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