The categories included overall value, voice service, data service, texting services, phone support, staff knowledge, and resolution of issues, and other customer support issues.
AT&T scored a 60/100, putting it 9 points behind T-Mobile, and 22 points behind the leader, US Cellular.
The U.S.' second largest carrier scored a 66 in 2009.
Consumer Reports says "AT&T is now the worst carrier." It is also the only carrier to see its numbers drop significantly from last year.
Apple iPhone owners were particularly displeased with AT&T, giving much lower scores than smartphone owners on other carriers.
AT&T responded: "We take this seriously and we continually look for new ways to improve the customer experience."