AT&T has the fastest data speed and web browsing for Apple's iPhone 4S, according to a recent study measuring the U.S. wireless carriers with the phone.

AT&T's data speed is considerably faster than Verizon's and Sprint's speed, according to mobile analytics firm Metrico Wireless. AT&T had an average download speed of 3,210 kilobits per second, compared to Verizon's 1071 kbps and Sprint's 581 kbps.

The average amount of time to load a page on AT&T's iPhone 4S was 1.29 seconds, twice as fast as Verizon's average time (2.60 seconds).

Verizon has the best call performance out of the three carriers, the study found. The call failure rate for Verizon's iPhone 4S was 2.1 percent, compared to 2.8 percent for AT&T and 3.7 percent for Sprint.

Verizon also had the best video quality. Metrico played YouTube clips on three carriers' iPhone4S, and the results showed that Verizon's video frame delivery rate was 96.08 percent, slightly better than AT&T's 95.98 percent. Sprint had a delivery rate of 87.08 percent.  

But Sprint did come out tops in terms of voice quality, which was stronger than AT&T on the uplink. However, on the downlink, AT&T had the advantage over Sprint, while Verizon had the weakest voice quality.  

In order to conduct the study, Metrico performed more than 21,000 web page downloads, ran more than 8,000 data download/upload tests, while mobile and stationary, and made approximately 6,000 voice calls on the iPhone4S.

Sprint started carrying the iPhone last month.. AT&T has carried the iPhone since 2007, while Verizon has carried the iPhone since February. Sprint-Nextel, the third largest wireless carrier. behind Verizon and AT&T, has struggled to retain customers in part because it didn't sell the iPhone. However, the company is looking to build a stronger customer base by offering unlimited data plans.