A reader has sent me details of speed testing on an iPhone4 in Dunedin, comparing networks.
The author also has a website, detailing the tests.
He notes these are not a general comparison of speeds between networks, but a comparison on the iPhone 4 only, in Dunedin. He did try six different locations there and his conclusion was that Telecom XT provides far greater speeds – but only in places where it works. In two places a good signal could not be located.