By Mikey Campbell

Published: 07:20 PM EST (04:20 PM PST)

A new study testing data speed, call reliability and voice quality, web browsing and video performance of Apple's iPhone 4S on the three major US carriers finds that AT&T's data speeds are the fastest, while Verizon takes the crown for having the least dropped calls.

Results from a study released on Friday reveal the strengths and weaknesses of the iPhone 4S on the three major cellular carriers in the US, AT&T, Sprint and Verizon, in an attempt to decipher which network boasts the best overall performance for the device, reports Computerworld.

The study by mobile performance analytics firm Metrico Wireless began in October, when all three major networks starting carrying the iPhone 4S, and surveyed data speeds, voice quality and voice call reliability in cities representative of a nationwide aggregate.

Tests were conducted using the company's global measurement system and consisted of over 20,000 web page downloads, 8,000 data download and upload tests both while moving and stationary and 6,000 voice calls. Voice quality was measured using the POLQA speech quality algorithm over the three carriers' networks.

The reported results come from a six-page summary released by Metrico, with the full 54-page report showing that each carrier has strengths in certain areas of operation. The firm sells its studies and findings to carriers and other telecom companies.

Amit Malhorta, Vice President of Marketing at Metrico, is quick to note that the study is not intended to necessarily find a winner among the three carriers, but "to provide objective data on how each carrier performs across important performance categories."

"We wouldn't be out to crown a single device the winner," Malhotra said. "We won't steer people to one phone or the other. We're not really trying to highlight the negatives."

In terms of data speeds, AT&T was the clear leader and had an average stationary download transfer rate of 3,210 Kbps, triple that of its closest competitor Verizon, while Sprint came in a distant third. Web browsing on the AT&T version of the iPhone 4S was also stellar, with load times averaging 1.29 seconds compared to Verizon's 2.60 seconds. Sprint averaged 6.44 seconds for page downloads.

Metrico rated data delivery as "excellent" across the board, though upload data speeds were left unreported.



The iPhone has had trouble with dropped calls in the past and Malhorta said that the 4S is no exception, showing a higher failure rate than the 1.4% industry average. In the test, Verizon had the least amount of dropped calls with 2.1% followed by AT&T and Sprint, with 2.8% and 3.7% respectively.

Uplink voice quality, when an iPhone user speaks, was a strong point for Sprint, scoring a 3.95 out of a possible 5 points with the Perceptual Objective Listening Quality Analysis algorithm Metrico employed for the study. AT&T scored 3.85 and Verizon 3.5. For incoming calls, voice AT&T took the top spot with a score of 3.82, followed by Sprint with 3.72 and Verizon with. 3.55.



When compared with other 3G smartphones in the carriers' lineups, the 4S was found to be a solid performer in terms of low noise and average bluetooth speech quality, but suffered in speakerphone speech quality.

Video performance was found to be fairly equal when Metrico delivered a 300 Kbps, 20 fps clip to the device. However, the firm noted that delivery success dropped somewhat for all three carriers with YouTube video clips.

Malhorta said that one of the intentions for the study was to show how performance problems in one city reported shortly after a phone is launched becomes less relevant over the entire network over time.

"We want to enable informed decisions on the part of subscribers," Malhorta said. "For carriers and OEMs, even though there are new features and functionalities rolling out, they can't forget about the core functions such as voice and data."

iPhone 4S carrier rankings by test

Data transfer rate (average/max)

• AT&T - 3210 Kbps/6047 Kbps
  
• Verizon - 1071 Kbps/2371 Kbps
  
• Sprint - 581 Kbps/1767 Kbps
  

Webpage load time

• AT&T - 1.29 sec.
  
• Verizon - 2.60 sec.
  
• Sprint - 6.44 sec.
  

Dropped call rate

• Verizon - 2.1%
  
• AT&T - 2.8%
  
• Sprint - 3.7%
  

Outgoing voice quality (out of possible 5 points)

• Sprint - 3.95
  
• AT&T - 3.85
  
• Verizon - 3.55
  

Incoming voice quality (out of possible 5 points)

• AT&T - 3.92
  
• Sprint - 3.72
  
• Verizon - 3.55
  

Video performance (success rate of delivery)

• AT&T and Verizon - >98%
  
• Sprint - 96.42%