Sears’ mobile site produced the fastest iPhone access time across all service providers among large web retailers in August, says Compuware. Last month, Sears.com produced an average iPhone mobile response time of 2.22 seconds.

Blockbuster.com came in second for iPhone testing with 4.51 seconds, followed by Williams-Sonoma.com (5.14 seconds), Rakuten.com (5.21) and BarnesandNoble.com (5.24).

Compuware measures the average iPhone response time for the three major service carriers: AT&T, Sprint and Verizon. Testing for the 20 retailers takes place once per hour per carrier from two U.S. locations (Virginia and California).

Gomez measures response time as the end-to-end time elapsed while downloading each mobile site.

Click here for full iPhone response time tests.