A survey of users of the four major cell phone providers in the U.S. has ranked AT&T, the exclusive carrier of Apple's iPhone, last in terms of customer satisfaction.

Consumer Reports surveyed more than 50,000 readers in 26 U.S. cities, asking about carriers in a number of different categories related to service and customer support. In 19 of those cities, AT&T ranked worst.

Overall, AT&T came in fourth place with a total score of 66. It ranked worst in voice service, and average for messaging and Web/e-mail. Customer service on the phone and via Web ranked poorly, as did staff knowledge and whether the customer's issue was resolved.

Coming in first was Verizon, which ranked highly across all categories: voice, messaging, Web/e-mail, and customer service. Verizon had an overall reader score of 75.

In second place was T-Mobile. Though customers feel the nation's smallest wireless carrier has decidedly average service, the customer support was found to be superior. It earned an overall score of 70.

Sprint came in third with a score of 67, with average service and sub-par customer support, particularly in the area of issue resolution.

The survey is not the only that has found customer satisfaction with AT&T to be relatively poor. In September, another survey found a significant decline in brand perception for AT&T after the carrier faced intense scrutiny over the quality of its network following the launch of the iPhone 3GS. That study found that AT&T lagged well behind competitor Verizon in terms of consumer perception.

AT&T's issues prompted the company to launch an aggressive public relations campaign in which the carrier publicly acknowledged customer complaints and promised to address them.

AT&T came under scrutiny again in October, this time directly from competitor Verizon, which launched a series of ads mocking the iPhone's "There's an app for that" tagline with the slogan "There's a map for that." The commercials, which contrast Verizon's 3G coverage map with AT&T's, have led to a lawsuit in which AT&T has alleged the TV spots are misleading.

This year, numerous reports (1, 2, 3) have suggested that a Verizon-compatible iPhone will arrive in the summer of 2010. For that to happen, Apple would have to build a new handset that could operate on Verizon's unique CDMA network.