By Philip Elmer-DeWitt
May 5, 2010

Three times as many as Verizon, according to a consumer survey released Tuesday

AT&T (T) announced in January that it was spending $2 billion this year to improve its much maligned cellular network.

But you wouldn’t know it from the survey of smartphone customers released Tuesday by ChangeWave Research, the consumer polling division of

In a poll that asked 4,040 smartphone users in March how many dropped calls they had experienced in the past three months, AT&T — the exclusive U.S. carrier of Apple’s (AAPL) iPhone and iPad mobile devices — came in dead last among the country’s four largest carriers.

Verizon (VZ) customers reported losing only 1.5% of their calls over the past three months, the lowest in the smartphone industry and the lowest percentage for a carrier ever recorded by ChangeWave.

AT&T customers, by contrast, reported 4.5% of calls dropped in the last three months. That’s one out of every 22 calls — three times as many as Verizon’s and the worst percentage ChangeWave has ever seen.

This is not good news for AT&T or for Apple, which has cited AT&T’s plans for improving its network as the reason it is sticking with the carrier — at least for now.

In the same survey, Sprint (S) was the country’s second most reliable carrier, with 2.4% of calls dropped, and T-Mobile (DT) the third, with 2.8% of calls dropped.

Below: A chart tracking the results of similar surveys dating back to Sept. 2008. It shows a growing number of dropped calls for AT&T and a steadily falling number for Verizon.

The number of calls that get dropped by one’s carrier correlates closely with overall satisfaction, according to ChangeWave, as evidenced by the chart below:

The survey was conducted between March 9 and March 23.

For other recent ChangeWave reports, see:

[Follow Philip Elmer-DeWitt on Twitter @philiped]

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