The Register reports that Eastern-European hackers have developed a new piece of kit that is being sold online. The TNT Instant Up can be used to flood phone numbers with calls, stopping the phone from being used until the device is turned off.
You can buy the device online, if you're so inclined.
Here's a video that the hackers have released, showing the device in action:
You might think that the Instant Up device is perfect for pranks, but it actually has a far more sinister use. Hackers can use TDoS (telephone denial of service) tools to take down crucial systems. IntelCrawler says that the FBI has identified TDoS attacks taking place last summer, and they were aimed at the healthcare sector. It also says that hackers have blocked a 911 emergency service in the US through the use of a similar device.