Dancho Danchev of Webroot posted information about an enhanced Telephony Denial of Service (TDoS) attack tool. You can find the specific post here:
In my Hacking Exposed: UC and VoIP book, I described a process for using Asterisk and a call generator along with SIP-based access to the voice network to launch TDoS attacks. This process is pretty easy to do, but not yet at the "script kiddie" level. It is certainly effective, but takes a little know-how.
The tool that Dancho describes is apparently much more turnkey. It is ready to go and appears to have preconfigured means to send calls into the network (Skype, vulnerable SIP servers, etc.), so it could pretty much be used by anyone. The tool also comes preconfigured with cellular access so it is more anonymous (although you can also easily get public wifi access on just about any street corner). The tool is also multi-threaded, which I assume means it can generate more concurrent calls through multiple origination points.
Many of the recent TDoS attacks are targeting a very small or even a single critical phone number, such as a hospital emergency room or ICU. Many of these attacks use cheap manual labor to generate the calls. The tool described above could easily be used for this same purpose, enabling many simultaneous attacks against many targets. If it can generate 100 concurrent calls, it could be used to attack up to 100 targets at a time. That is a much better model than hiring 100 people to be on the phone.