Consumer Reports, the influential product review publication, says AT&T Inc. is again the worst-rated cellular service provider in the U.S., a blow to the carrier's effort to rehabilitate its network and reputation.

The conclusion, based on a survey of 58,000 readers, shows customers continue to hold AT&T's service in low regard even after the carrier boosted its wireless spending by $2 billion this year in an effort to correct what it has acknowledged were weaknesses in its network.

The results bode poorly for AT&T as it faces possible competition for Apple Inc.'s iPhone, a device it carries exclusively now and relies on for much of its subscriber growth. In fact, Consumer Reports found "iPhone owners were, by far, the least satisfied with their carrier."

"We take this seriously, and we continually look for new ways to improve the customer experience," AT&T said in an emailed statement. The carrier pointed to its success attracting customers and claimed its dropped-call rate is only slightly worse than the best in the industry.

Apple is making a version of the iPhone that Verizon Wireless, the country's largest wireless carrier, will sell early next year, people familiar with the matter have said.