Phreaking or phone freaking has been the begining of the hacking culture. "The term first referred to groups who had reverse engineered the system of tones used to route long-distance calls. By re-creating these tones, phreaks could switch calls from the phone handset, allowing free calls to be made around the world." ( Wikipedia ) OK, you cannot phone for free by whisteling in your android device. But try this: Type *#*#4636#*#* in your smartphone and you find a secret menu. There are many other secret codes, including functions to reset the entire device in fabrique state. Even more spooky: Some webpages simulate the dialing of these numbers. So surfing the web with your smartphone may cause seriouse trouble. Taken from Wizzywig .