If you use your iPhone to connect to open or public Wi-Fi networks, it’s a good idea to tell the device to forget the networks name after youre done using it. An attacker could abuse this behavior to sniff the network for passwords and other sensitive information transmitted from nearby iPhones even when the owners of those phones have no intention of connecting to a wireless network, simply by giving his rogue access point a common name. This could create a privacy problem for those who are using the iPhone’s 3g data connection to send e-mail or other information.”]
Source: https://krebsonsecurity.com/2010/06/wi-fi-street-smarts-iphone-edition/