Hackers build private 'Ninja Tel' phone network at Defcon

Essentially ...

"The phones are HTC One V phones running Android 4.0.3. Calls can be routed over the private GSM network or over Defcon's Wi-Fi network. The network is not encrypted and there is no emergency call phone number.

The "Ninja Tel" network is "the biggest open BTS (base transceiver station) network ever," said Ninja Michael J.J. Tiffany. BTS networks are designed to allow for software-based switching technology that can be housed in small spaces, such as a van."