For those not familiar with STIR, it is an effort (working group) attempting to solve the issue of spoofed calling number (caller ID). It has become so easy to generate calls with random anonymous numbers or specific/targeted spoofed numbers, that the source number has lost most of its value as an indicator of who is calling. This enables some attacks, but more importantly, makes other attacks such as Telephony Denial of Service (TDoS), voice SPAM (robocalls), scams, voice phishing (vishing), and harassing/threatening calls much more of an issue.
I just finished attending the 2014 SIP Network Operators Conference (SIPNOC). I couldn't attend some of the conference and missed the update on the Secure Telephony Identify Revisited (STIR). However, I checked the checked the IETF website and there has been quite a bit of activity and there are several new documents that are worth a read. You can find these documents at:
Wardialing and modems are still a reality despite the wide adoption of VoIP. Also, the available of VoIP at the war dialing tool side, has made this process more effective. Plus, the tools mentioned can be used for a lot of things other than war dialing, including nasty things like looking for second dial tone, IVR behaviors, etc. that can be used for other attacks.
I covered how to use tools like WarVOX for these attacks in my Hacking Exposed: UC and VoIP book:
Patrick McNeil covers how to hack SIP servers, at service providers and enterprises, to make money. The presentation is useful because it covers why someone might bother to hack these servers, namely:
Toll fraud or International Revenue Sharing Fraud (IRSF) - basically using someone elses PBX to generate calls to premium numbers set up by the hacker or where the hacker has an agreement with the owner to generate traffic.
Telephony Denial of Service (TDoS) - using someones PBX to target a business or individual. The attacker makes money through extortion.
Robocalling/SPAM - using someone's PBX to make many SPAM or vishing calls to individuals (this was briefly mentioned).
At the end of the presentation, there is a brief TDoS demo.
Note that another way to make money is call pumping, where the calls are to 1-800 numbers and the attacker gets a share of the revenue, but this arrangement is more difficult to set up.