Hey, it's your Ninja

From a corner of the vendor room at Defcon 20, a repurposed van sporting a "Ninja Tel" logo and a 12-foot cell phone tower broadcasts a GSM signal. It's available only to attendees lucky enough to score a Ninja Phone from the Ninja hacker group.

There's more than just a standard GSM network powering the Ninja Tel network. Ninja Tel uses a little-known feature of Android 4.0 Ice Cream Sandwich that allows networks to route calls over GSM or onto Wi-Fi, if the Wi-Fi has been configured properly using Session Initialization Protocol (SIP) and has a SIP Server.