I’ve heard reports that iPhone web surfing traffic is orders of magnitude more than other smartphones. Given that it’s not a crippled browser like on my previous Sony Ericsson or Blackberry it’s not surprising.
Checking the usage counters on my (second) iPhone, I’ve used 466M down and 74M up via the EDGE network since I got it 6 months ago. It doesn’t monitor WiFi traffic. While it does check mail, it only gets headers unless I pull up a message so most of that is web traffic. Nothing spectacular, but I find it pretty interesting.