Sniffing Open WiFi Networks is Not Wiretapping
 

A federal judge in Illinois has ruled that the act of intercepting unencrypted WiFi traffic does not constitute wiretapping. This decision may have far flung repercussions, setting the stage for future court battles. It's not illegal to intercept communications "made through an electronic communication system that is configured so that such electronic communication is readily accessible to the general public."

http://www.hardocp.com/news/2012/09/...s_wiretapping/