iPhones running OS 3 have a usability feature where Safari is launched immediately when joining a network. This allows rogue access points a known vector of attack.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/78968/iphone-pwnability.txt
Source: https://packetstormsecurity.com/files/78968/iPhone-Safari-Auto-Open.html