AT&T is the worst cellphone service provider in the US, according to Consumer Reports. The conclusion is based on a survey of almost 58,000 people, more than half of which are iPhone owners (AT&T is the exclusive service provider of Apple's phone).

AT&T struggled in all 10 categories used to determine the rankings. U.S. Cellular was the top-rated provider with 82 points of satisfaction. Verizon Wireless and Sprint are neck-and-neck with 74 points and 73 points, respectively. T-Mobile was a bit further behind with 69 points and AT&T brought up the rear with 60 points.

To make matters worse for the company, it was the only wireless carrier to show a significant satisfaction decrease in the survey. Last year, AT&T had a rating of 66. Verizon dropped to second place after being the leader in most of the annual Consumer Reports ratings since 2003.

Most AT&T users complain that the company can't keep up with their heavy data usage. It also doesn't help that other networks are ahead of AT&T in offering 4G capabilities to their customers.

Consumer Reports found that iPhone owners were much less satisfied with their carrier; they rated their data service lower than owners of smartphones on other carriers. This could be particularly bad for AT&T if the rumored Verizon iPhone hits stores in early 2011. "Our survey suggests that an iPhone from Verizon Wireless, which is rumored, could indeed be good news for iPhone fans," Paul Reynolds, Electronics Editor for Consumer Reports, said in a statement.

"We take this seriously and we continually look for new ways to improve the customer experience," an AT&T spokesperson said in a statement. "The fact is wireless customers have choices and a record number of them chose AT&T in the third quarter, significantly more than our competitors."