Now that the iPhone 4S is available on three major national carriers, which network is best? Several blogs have begun testing the network speeds, and early results indicate that AT&T is the fastest for the iPhone 4S. Having asked more than 4,000 users to test their iPhone 4S speed, Gizmodo finds an average speed (in kilobits per second) of 2,617.2 for AT&T, versus 2,272.0 for Verizon and 1,673.6 for Sprint. AT&T also has the fastest speed, reaching 13,973.6 kilobits per second versus 13,810.3 for Sprint and 13,473.4 for Verizon. iDownload blog also says that AT&T has the fastest download speed (as opposed to its speed for Web browsing).