I assume most everyone has seen the FBI press release on Telephony Denial of Service (TDoS). For those who have not, see:

http://newark.fbi.gov/pressrel/pressrel10/nk051110.htm

I am also seeing the term used to describe enterprise-directed DoS, where an attacker typically floods a contact center with calls. I have recently worked with both enterprises, service providers, and hosted IVR companies that have seen these attacks. The current motive seems to be traffic pumping/revenue generation, not DoS per se, but the side impact is that operation at the target sites is degraded or seriously disrupted, depending on call volume and trunk capacity. Interestingly, the targets I have talked to are primarily using TDM trunks, while the attackers (according to the service providers I have talked to) are using VoIP. I have a post on my blog with more information:

http://voipsecurityblog.typepad.com/marks_voip_security_blog/2010/06/more-on-telephony-dos-tdos.html

Is anyone else seeing these attacks?